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NOVA (not a acronym) is the food classification that categorizes foods based on the degree and purpose of food processing, rather than their nutritional content. It was developed in 2009 by a research group at the University of São Paulo in Brazil[2].

NOVA classifies foods into four groups based on the nature, extent, and purpose of the industrial processing they undergo.

(1)Unprocessed or minimally processed foods
Fresh fruits and vegetables, and other natural foods (such as grains, milk, fish, and meat) that have undergone processes like removing inedible parts, drying, grinding, pasteurization, chilling, freezing, or vacuum-packaging.

(2)Processed culinary ingredients
Substances derived from Group 1 foods or from nature through processes that include pressing, refining, milling, or drying, such as oils, butter, sugar, and salt. These processed culinary ingredients are typically not consumed on their own.

(3)Processed foods (PFs)
These are typically made by adding Group 2 substances to Group 1 foods. Examples include canned vegetables, fruit in syrup, canned fish, cheese, and freshly made breads.

(4)Ultra-processed foods (UPFs)
These are formulations created by combining many ingredients and undergoing a sequence of industrial processes. Examples include breakfast cereals, soft drinks and fruit juices, sweet or savory snacks, confectioneries, instant foods, reconstituted meat products such as sausages and nuggets, and most fast food items[3,4].

Food processing, in essence, refers to “various operations by which raw foodstuffs are made suitable for consumption, cooking, or storage,” and virtually all foods undergo some form of processing before being eaten. Therefore, processing itself is not inherently bad. 

However, ultra-processed foods are not modified foods but formulations made mostly or entirely from substances derived from foods and additives through multiple industrial processes, with little to no Group 1 natural foods[3].

UPFs are highly appealing because they are hyper-palatable and addictive, inexpensive, have a long shelf life, and can be consumed anytime, anywhere[3].

The evidence based on the NOVA classification so far suggests that the decline in minimally processed foods and home cooking, alongside the replacement of food supplies with ultra-processed foods, is associated with unhealthy nutritional profiles and an increase in several diet-related diseases[3].

In studies on adults reporting the proportion of total daily energy intake from UPFs, the highest levels (on average) were reported in the USA (55.1–56.1%), followed by the UK (53–54.3%), Canada (45.1–51.9%), France (29.9–35.9%), Brazil (20–29.6%), Spain (24.4%), and Malaysia (23%)[6].

A cross-sectional study (2005–2014) on American adults, who were found to consume an average of  56.1% of their total energy intake from UPFs, revealed significant differences across quintiles. Those in the highest quintile (Note 1) consumed 84.5% of their total energy intake from UPFs, while those in the lowest quintile accounted for 25.4%[7]. 

 (Note 1: Quintile refers to one of five equal measurements that a set of things can be divided into)

♦A cross-sectional time series study conducted in fifteen Latin American countries revealed that sales of UPFs were associated with changes in body weight in twelve of these countries from 2000 to 2009[8].

A cross-sectional study based on data from Brazil’s 2008–2009 Household Budget Survey found that household availability of UPFs was positively correlated with both the average BMI and obesity prevalence. Those in the highest quartile (Note 2) of household consumption of UPFs were 37% more likely to be obese compared to those in the lowest quartile[9]. 

(Note 2: Quartile refers to one of four equal measurements that a set of things can be divided into)

♦A study involving 6,143 participants from the UK National Diet and Nutrition Survey (2008–2016) classified foods recorded in four-day food diary according to the NOVA system. Consumption of UPFs was associated with increases in BMI, waist circumference, and obesity rates in both men and women. For every 10% increase in UPF consumption, the obesity rate increased by 18%. 

Higher consumption of UPFs was observed among men, white British individuals, smokers, younger people, and those in lower social class groups[10].

♦A cross-sectional study involving 19,363 adults aged 18 and older from the 2004 Canadian Community Health Survey, found that individuals in the highest quintile of UPF consumption were 32% more likely to be obese compared to those in the lowest quintile. Higher UPF intake was associated with being male, younger age, lower educational attainment, physical inactivity, smoking, and being born in Canada[4].

♦A prospective cohort study conducted since 1999 among graduates of the University of Navarra in Spain tracked 8,451 participants who were not overweight at baseline for about nine years. Those in the highest quartile of UPF consumption had a 26% higher risk of developing overweight or obesity compared to those in the lowest quartile.

Moreover, on average, they consumed more fast food, fried foods, processed meats, and sugar-sweetened beverages, while, in contrast, their vegetable intake was the lowest. A higher consumption of UPFs was associated with lower adherence to the Mediterranean diet[11].

♦A U.S. research group analyzed data on 5,919 children and 10,064 adults from the National Health and Nutrition Examination Survey (2015-2018) to investigate the relationship between UPF consumption and overall diet quality. Diet quality was assessed using the American Heart Association (AHA) diet score and Healthy Eating Index (HEI)-2015 score.

The research group concluded that higher consumption of UPFs was associated with substantially lower diet quality among children and adults. These findings were consistent with previous studies conducted in several countries[12].

♦An Italian research group hypothesized that meal timing could also be linked to food processing and conducted a study to test this. They analyzed data on 8,688 individuals from the Italian Nutrition & Health Survey (INHES), conducted between 2010 and 2013. Subjects were classified as early or late eaters based on the population’s median timing for breakfast, lunch, and dinner.

Results showed that late eaters (breakfast after 7 AM, lunch after 1 PM, and dinner after 8 PM) were less likely to consume unprocessed or minimally processed foods compared to early eaters, while they consumed more processed foods (PFs) and UPFs. Late eating was also inversely associated with adherence to the Mediterranean diet[13].

The Mediterranean diet, which primarily consists of fruits, vegetables, legumes, nuts, olive oil, and fish, has been shown to be linked to reduced weight gain[14].

A group of researchers in the U.S. conducted a crossover comparative study to ascertain the net energy intake of two different diets: one consisting of specific processed foods and the other of an isocaloric whole-food (WF) diet. Eighteen subjects consumed two types of sandwiches with the same calorie content but differing in processing levels.

The WF meal consisted of multigrain bread (containing whole sunflower seeds and whole-grain kernels) and cheddar cheese, while the PF meal consisted of white bread and a processed cheese product.

In this study, diet-induced thermogenesis (DIT)(Note 3) after consuming the PF meal was 46.8 % lower than that of the WF meal. The researchers concluded that this difference in DIT led to a 9.7 % increase in net energy-gain for the PF meal[15].

(Note 3)  Diet induced thermogenesis (DIT) is the process by which the body increases its energy expenditure for several hours in response to food intake.

Regarding the significant reduction in diet-induced thermogenesis (DIT) observed with the PF meal, the researchers provided the following analysis:

Compared to whole foods, PFs are characterized by lower nutrient density (a lower content and diversity of nutrients per calorie), less dietary fiber, and an excess of simple carbohydrates. As a result, PFs are structurally and chemically simpler than whole foods, making them easier to digest[15,16].

A group of U.S. researchers conducted a randomized controlled trial to determine the effects of ultra-processed versus unprocessed diets on ad libitum energy intake in twenty adults with stable body weight. Subjects were randomly assigned to either the ultra-processed or calorie-matched unprocessed diet for two weeks, followed by the alternate diet for another two weeks.

In this experiment, participants were allowed to eat additional food after meals. As a result, they consumed more energy (459±105 kcal /day) during the ultra-processed diet and gained 0.4±0.1 kg of body fat. In contrast, they lost 0.3±0.1 kg of body fat during the unprocessed diet.

Fasting blood tests showed that levels of the appetite-suppressing hormone peptide YY (PYY) increased during the unprocessed diet as compared with both the ultra-processed diet and baseline. Also, levels of the hunger hormone ghrelin decreased during the unprocessed diet compared to baseline. This suggests that participants felt less hungry during the unprocessed diet, whereas the ultra-processed diet provided less satiety, making participants feel hungrier[19]. 
           

I would like to explain the link between consumption of UPFs and an increase in obesity from the perspective of intestinal starvation.

Since the development of the NOVA classification, various studies have focused on the degree of food processing rather than calorie content, which is noteworthy.

Through this blog, I have explained that a combination of factors—such as an unbalanced diet leaning toward refined carbohydrates and UPFs, a lack of vegetables, and an irregular lifestyle—can induce intestinal starvation, potentially raising the body's set-point weight.

UPFs are often high in energy density, so they are generally believed to promote obesity when overeaten. However, I believe the biggest issue is the "ultra-processing" itself, as these foods are digested and absorbed more quickly than natural foods.

If the diet is skewed toward refined carbohydrates and UPFs, and the overall diet quality declines, blood sugar levels can fluctuate sharply. Additionally, since these foods leave nothing behind in the intestines after digestion, intestinal starvation can be triggered (Note 5).

The fact that adherence to the Mediterranean diet and the consumption of natural foods like vegetables are inversely correlated with obesity supports my perspective.

In Japan, In my opinion, the consumption of UPFs such as instant foods, cookies, sweet bread, and chocolate confection is not necessarily low. However, one reason Japan’s obesity rate is lower than in Western countries may be its rice-based food culture, and the fact that many Japanese people still follow traditional eating habits. 

(Note 5: Foods high in fat, such as ice cream, take longer to digest and may help prevent intestinal starvation.)

The World Obesity Federation (WOF) warns that if policy directions remain unchanged and no effective measures are taken to prevent and treat obesity, more than half of the global population will be classified as overweight or obese by 2035.

I think this suggests that past policies focused solely on "calories in/ calories out" have not been particularly effective. 

What we need now is a shift in focus from "calories" to factors such as the degree of food processing, the number of chews, and digestibility in policymaking.

However, many people today prefer soft foods that require little chewing and have become overly reliant on refined carbohydrates and UPFs. These diets are low in nutrients and fiber, making them easy to digest, allowing the body to absorb large amounts of energy with minimal effort.

Moreover, once all the food is fully digested in the intestines, a signal that “there is no food” might be sent to the brain.

Such dietary habits were likely rare, if not nonexistent, in human history—at least until around 1970. It is not an overstatement to say that the sharp rise in being overweight, obesity, and many lifestyle-related diseases coincided with the rapid industrialization of food processing in the 1970’s and 80’s.
               

<References>
[1]Katz DL, Meller S. Can we say what diet is best for health?  Annu Rev Public Health. 2014;35:83-103. 

[2]Monteiro CA et al. NOVA. The star shines bright. Food classification. Public Health. World Nutr. J. 2016, 7, 28–38.

[3]Monteiro CA et al. The UN Decade of Nutrition, the NOVA food classification and the trouble with ultra-processing. Public Health Nutr. 2018 Jan;21(1):5-17. 

[4]Nardocci M et al. Consumption of ultra-processed foods and obesity in Canada. Can J Public Health. 2019 Feb;110(1):4-14. 

[5]Fiolet T et al. Consumption of ultra-processed foods and cancer risk: results from NutriNet-Santé prospective cohort. BMJ. 2018 Feb 14;360:k322. 

[6]Elizabeth L et al. Ultra-Processed Foods and Health Outcomes: A Narrative Review. Nutrients. 2020 Jun 30;12(7):1955. 

[7]Juul F et al. Ultra-processed food consumption and excess weight among US adults. Br J Nutr. 2018 Jul;120(1):90-100. 

[8]Ultra-processed food and drink products in Latin America: trends, impact on obesity, policy implications. Pan American Health Organization, Washington (DC) (2013)

[9]Canella DS et al. Ultra-processed food products and obesity in Brazilian households (2008-2009). PLoS One. 2014 Mar 25;9(3):e92752. 

[10]Rauber F et al. Ultra-processed food consumption and indicators of obesity in the United Kingdom population (2008-2016). PLoS One. 2020 May 1;15(5):e0232676. 

[11]Mendonça RD et al. Ultraprocessed food consumption and risk of overweight and obesity: the University of Navarra Follow-Up (SUN) cohort study. Am J Clin Nutr. 2016 Nov;104(5):1433-1440. 

[12]Liu J et al. Consumption of Ultraprocessed Foods and Diet Quality Among U.S. Children and Adults. Am J Prev Med. 2022 Feb;62(2):252-264. 

[13]Bonaccio M et al. Association between Late-Eating Pattern and Higher Consumption of Ultra-Processed Food among Italian Adults: Findings from the INHES Study. Nutrients. 2023 Mar 20;15(6):1497. 

[14]Beunza JJ et al. Adherence to the Mediterranean diet, long-term weight change, and incident overweight or obesity: the Seguimiento Universidad de Navarra (SUN) cohort.  Am J Clin Nutr. 2010 Dec;92(6):1484-93. 

[15]Barr SB, Wright JC. Postprandial energy expenditure in whole-food and processed-food meals: implications for daily energy expenditure. Food Nutr Res. 2010 Jul 2;54. 

[16]Fereidoon Shahidi. Nutraceuticals and functional foods: Whole versus processed foods. Trends in Food Science & Technology, Volume 20, Issue 9, 2009, Pages 376-387.　

[17]Secor SM. Specific dynamic action: a review of the postprandial metabolic response. J Comp Physiol B. 2009 Jan;179(1):1-56. 

[18]Roberts SB. High-glycemic index foods, hunger, and obesity: is there a connection? Nutr Rev. 2000 Jun;58(6):163-9. 

[19]Hall KD et al. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab. 2019 Jul 2;30(1):67-77.e3. 

[20] World Obesity Federation. 
　　　　

As I've explained in previous blog posts, I believe that each person has an individual “set-point” for their weight, and that understanding how this set-point increases is the key to addressing the issue of obesity. 

This time, I would like to share my thoughts on recent advances in research regarding the set-point theory of body weight, as well as the environmental and behavioral factors that influence it.

<Obesity and weight loss attempts> 

♦A fat person who insists that a lean friend has consistently eaten more than the fat person does, may well be telling the truth.（*snip*）

The group of obese patients who are greatly in need of our understanding are those who keep to a calorie intake of perhaps 1000 kcal per day, yet lose less than one kg per week. There is no doubt whatsoever that such people exist, and can be studied in a metabolic ward under conditions where 'cheating' is virtually impossible without being detected. Usually these are middle-aged women who have been perhaps 40 kg overweight, and who have already lost about 20 kg. They are often depressed, hypothermic, and have a low metabolic rate. The nature of this metabolic adaptation to a low calorie diet is not known (as of 1973), but it is a phenomenon which has been known since before 1920. [1](J S Garrow, 1973)　

♦For obese individuals, a certain amount of weight loss is possible through a range of treatments, but long-term sustainability of lost weight is much more challenging, and in most cases, the weight is regained [2]. In a meta-analysis of 29 long-term weight loss studies, more than half of the lost weight was regained within two years, and by five years, more than 80% of lost weight was regained [3,4].

In addition, studies of those who are successful at sustained weight loss indicate that the maintenance of a reduced degree of body fatness will probably require close attention to energy intake and expenditure, perhaps for life[5].

Contrary to popular belief, people with obesity generally have a higher absolute REE compared to leaner subjects.This is because obesity increases both body fat and metabolically active fat-free mass[7,8].

PAEE can be subdivided into "voluntary exercise" and “activities of daily living.” Despite typically engaging in less physical activity, obese individuals often have a daily energy cost for physical activity similar to that of non-obese individuals since PAEE is proportional to body weight [7,9]. Additionally, due to a greater food intake, their DIT also tends to be higher [7].

<Dynamic changes in energy expenditure>

♦Obesity prevention is often erroneously described as a simple bookkeeping matter of balancing caloric intake and expenditure [10].

In this model, energy intake and expenditure are considered independent parameters determined solely by behavior. It is assumed that an obese person can steadily lose weight by eating less and/or moving more at a rate of one pound for every 3,500 kcal (or one kg for every 7,200 kcal) of accumulated dietary caloric deficit [7,11]. This view has been referred to as a “static model” of weight-loss, but it has been shown to be physiologically impossible [7,12]. 

<Set-point theory of body weight>

♦In recent years, the influence of homeostatic control has been recognized, and there is growing evidence that the body employs physiological mechanisms to manipulate energy balance and maintain body weight at a genetically and environmentally determined "set-point."[12] 

In 1953, Kennedy proposed that body fat storage is regulated [15]. In 1982, nutritional researchers William Bennett and Joel Gurin expanded on Kennedy's concept when they developed the set-point theory [16]. The model has been widely adopted, and strengthened particularly after the discovery of leptin in the 1990’s [7,12].

When an individual loses weight, the body significantly reduces energy expenditure to a degree that is often greater than predicted based on changes in body composition or the thermic effect of food. It also causes an increase in appetite through hormonal regulation and alters food preferences through behavioral changes, to drive the body weight back toward its set-point range[7,16]. 

♦Maintenance of a 10% or greater reduction in body weight in lean or obese individuals is accompanied by  about 20 to 25% decline in 24-hour energy expenditure. This reduction in weight maintenance calories is 10 to 15% lower than what is predicted based solely on alterations (/changes) in fat and lean mass [17,18].

Since obese individuals also display these compensatory metabolic adjustments in response to dietary restriction, obesity may be considered a natural physiological state for some people. Experimental studies on obesity in animals similarly suggest a view of obesity as a condition of body energy regulation at an elevated set-point [19]. 

♦A meta-analysis of cross-sectional studies investigating adaptive thermogenesis (AT) by comparing formerly obese subjects who had lost weight with BMI-matched subjects who were never obese, reported a 3–5 % lower resting energy expenditure (REE) in formerly obese subjects compared to never obese controls[20].

This effect means, for example, that if an obese woman reduced her weight from 100kg to 70kg, she would have to consume fewer calories to remain at 70kg than a woman who had consistently weighed 70kg[6]. Similar results have been confirmed in animal experiments involving obese and normal-weight rats.

This suggests that the frequent claim made by obese people that they eat the same or less than their lean friends but lose no weight, must be given more credence than it is ordinarily accorded[19].

♦In addition, hyperphagia (overeating) has been demonstrated following experimental semi-starvation and short-term underfeeding, which is probably the result of homeostatic signals resulting from the loss of both body fat and lean tissue [7,21].

　
♦This theory also suggests that a person's set-point for body weight is established early in life and remains relatively stable unless altered by specific conditions. However, the set-point may change throughout one’s life due to factors such as marriage, childbirth, menopause, aging, and disease [16]. 

On the other hand, the set-point theory remains a theory because all the molecular mechanisms involved in set-point regulation have not been elucidated, and some researchers may consider this theory to be overly simplistic[16].

However, some researchers have pointed out problems with the set-point model of regulation.

If such a powerful biological feedback system regulating the state of our body fat exists, then why do many individuals in most Western countries gain weight throughout majority of their lives？ In particular, they argue that this model cannot explain the increasing prevalence of obesity that has been observed in many societies worldwide since the 1970’s[22].

    
In response, some researchers argue that while metabolic resistance to sustaining a reduced body weight is strong, metabolic resistance to sustained increased adiposity may not be physiologically long-lasting. The steadily increasing prevalence of obesity in humans also suggests that the state of body fat is facilitated more vigorously than losing weight[17,23].

■These explanations may sound reasonable at first, but in my opinion, this is no longer a "set-point"  and it fails to explain why the body stubbornly shows metabolic resistance to maintaining weight loss, even at a higher set-point weight. 

When applied to humans, not everyone who frequently consumes high-calorie foods becomes obese. This brings up several contradictions, such as: 

(1)Why is obesity more prevalent among the lower-income groups in Western societies[22,27] and relatively wealthier groups in developing societies?[28]; 

(2)The coexistence of undernutrition and obesity in poor populations, observed globally since the 1950’s[29]; 

(3) Why do some people gain weight after environmental changes such as entering college, getting married, having children, or moving from Asia to Western countries?[22]

As I have mentioned repeatedly in this blog, I believe that an increase in set-point for body weight is due to inducing intestinal starvation, and that I can explain all these contradictions. 

In the following section, I will explain that more specifically.

In 2012, the American Association of Clinical Endocrinology (AACE) designated obesity as a chronic disease. One of the rationale for that designation is that, like other chronic diseases, the pathophysiology of obesity is complex, involving interactions of genetic, biological, environmental, and behavioral factors[30].

Some researchers interested in the body weight set-point theory argue that understanding how genes and the environment interact to regulate the set-point is essential to determining whether obesity, as a chronic disease, can be cured. However, they struggle to explain the many significant environmental and social influences[22].

■ I also believe that the set-point of body weight changes due to the interaction between (1) genetic and biological factors, and (2) environmental and behavioral factors, but this time, I will mainly discuss (2) in this article.

When considering changes in living environment since the 1970’s, most researchers blame the rise in obesity on the increased availability of high-calorie foods and a decrease in physical activity as society became more affluent. In other words, they believe that a positive energy balance is necessary for weight gain.

However, paradoxically, the fact that the increasing prevalence of obesity coincides with an increase in weight-loss attempts[31] suggests that our understanding of energy balance may be flawed[12].

As suggested by overfeeding experiments, “temporary weight gain from overeating” and “irreversible weight gain occurring over many years ” are different. In my view, obesity as a chronic disease arises rather from signals of negative energy balance or "food scarcity" in the body, as in the cases where people gain more weight than before after starvation or dieting.

[Related article]
The Overfeeding Study Suggests That "Overeating" Is Not the Cause of Obesity
           

■Despite its impact on our bodies due to changes in our living environments since the 1970’s, "intestinal starvation" remains unrecognized. 

Intestinal starvation refers to a state where everything consumed is fully digested throughout the entire intestinal tract, and it can occur in today's affluent developed countries, developing countries, or even among the poor. When there is little or no fiber and everything has been digested, our bodies perceive it as having "no food."

【Related Article】
The Body Perceive That It Is More Starved than in the Past

     
Perhaps in many parts of the world before 1970, even if people went a whole day without eating until their next meal, there were likely still undigested substances like fiber and tough plant cell walls left in their intestines. However, in today’s society, with its abundance of easily digestible, refined carbohydrates, processed foods, and fast food, intestinal starvation can occur in as little as eight to ten hours, depending on eating habits. 

Intestinal starvation is more likely to occur with frequent consumption of easily digestible refined carbohydrates (bread, noodles, rice, etc.), industrially processed meat or fish products, fast food, and snacks, etc., combined with a lack of vegetables and long periods of prolonged hunger (such as skipping breakfast, late-night meals, or irregular eating habits).

【Related Article】

 Three (+one) Factors to Accelerate “Intestinal Starvation”
     

■In the animal experiments on rats described in section 2 above, it was reported that consuming a "high-energy diet" for 90 days led to irreversible weight gain, suggesting an increase in the set-point. However, the "fattening” diet used in this experiment (Rolls et al., 1980) primarily consisted of highly palatable items like potato chips, cheese crackers, and cookies sold in supermarkets. Those foods contained 47.5% industrially processed refined carbohydrates (fat: 42%, protein: 10.5%) on an energy basis[25]. Moreover, rats only eat when they’re hungry, and they are capable of eating the same food repeatedly.

In contrast, the “chow” fed to the control rats may have been made from ingredients like ground wheat, ground corn, soybean meal, and fish meal, etc. In other words, just as our diets from over fifty years ago, it likely contained a high amount of indigestible components, such as fiber and tough plant cell walls.

Therefore, I question the conclusion that highly palatable "high-energy diets" alone caused the irreversible weight gain.
     

Below, I will explain the mechanism by which the set- point for body weight increases due to the induction of intestinal starvation. While some of it involves speculation, it is based on events that have happened to me several times. You may not believe it, but at least for me, it is 100% accurate.

   
■Let's assume there is a man who has maintained a weight of 70 kg for many years. Even though his weight may fluctuate slightly during busy periods or after overeating, his weight revolves around 70 kg, so his set-point would be considered 70 kg.

(Normally, a few undigested fiber or fats may remain, but when all food is perfectly digested, 5 to 10 kg of weight gain over a short period is possible.)

Once the body’s balance point rises, it becomes harder to lose weight because the overall absorption ability has increased. As mentioned in reference in section 1 , I agree with the idea that obesity is a “state of energy regulation at a higher set-point,” and is "a natural physiological condition" for obese individuals.

For more details, please refer to the article below.

【Related Article】
  Gaining Weight by Intestinal Starvation; What Does It Mean?

It may be difficult to determine the exact cause when someone gains a few kg in a year, meaning their highest weight ever. However, I believe that, even with reduced calorie and carbohydrate intake from the meals I provide, it is possible to significantly increase a person's weight (by around 5 to 10 kg) within a few months, setting a new high set-point weight. By observing the data before and after, I think it is possible to investigate what changes have occurred inside the body.
       

<References>

[1]Garrow JS. Diet and obesity. Proc R Soc Med. 1973 Jul;66(7):642-4. PMID: 4741395; PMCID: PMC1645095.

[2]Wu T, Gao X, Chen M, van Dam RM. Long-term effectiveness of diet-plus-exercise interventions vs. diet-only interventions for weight loss: a meta-analysis. Obes Rev. 2009;10(3):313–323. 

[3] Hall KD, Kahan S. Maintenance of Lost Weight and Long-Term Management of Obesity. Med Clin North Am. 2018 Jan;102(1):183-197. 

[4]Anderson JW, Konz EC, Frederich RC, Wood CL. Long-term weight-loss maintenance: a meta-analysis of US studies. Am J Clin Nutr. 2001 Nov;74(5):579-84. 

[5]Wing RR, Hill JO. Successful weight loss maintenance. Annu Rev Nutr. 2001;21:323-41. 

[6]Jou C. The biology and genetics of obesity--a century of inquiries. N Engl J Med. 2014 May 15;370(20):1874-7. 

[7]Hall KD, Guo J. Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. Gastroenterology. 2017 May;152(7):1718-1727.e3. 

[8]Nelson KM, Weinsier RL, Long CL, et al. Prediction of resting energy expenditure from fat-free mass and fat mass. Am J Clin Nutr. 1992;56:848–856.

[9]Westerterp KR. Physical activity, food intake, and body weight regulation: insights from doubly labeled water studies. Nutr Rev. 2010;68:148–154.

[10] Levine DI. The curious history of the calorie in U.S. policy: a tradition of unfulfilled promises. Am J Prev Med. 2017;52:125–129.

[11] Hall KD, Chow CC. Why is the 3500 kcal per pound weight loss rule wrong? Int J Obes (Lond). 2013 Dec;37(12):1614. 

[12] Egan AM, Collins AL. Dynamic changes in energy expenditure in response to underfeeding: a review. Proc Nutr Soc. 2022 May;81(2):199-212. doi: 10.1017/S0029665121003669. Epub 2021 Oct 4. PMID: 35103583.

[13]Thomas DM, Martin CK, Lettieri S et al. (2013) Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. In Int J Obes 37, 1611–1613.)

[14]Hall KD, Heymsfield SB, Kemnitz JW et al. Energy balance and its components: implications for body weight regulation. Am J Clin Nutr. 2012 Apr;95(4):989-94. 

[15]KENNEDY GC. The role of depot fat in the hypothalamic control of food intake in the rat. Proc R Soc Lond B Biol Sci. 1953 Jan 15;140(901):578-96. 

[16] Ganipisetti VM, Bollimunta P. Obesity and Set-Point Theory. 2023 Apr 25. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 37276312.

[17] Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans. Int J Obes (Lond). 2010 Oct;34 Suppl 1(0 1):S47-55. 

[18] Leibel R, Rosenbaum M, Hirsch J. Changes in energy expenditure resulting from altered body weight. N Eng J Med. 1995;332:621–28.

[19] Richard E. Keesey, Matt D. Hirvonen, Body Weight Set-Points: Determination and Adjustment, The Journal of Nutrition, Volume 127, Issue 9, 1997, Pages 1875S-1883S, ISSN 0022-3166.

[20]Astrup A, Gøtzsche PC, van de Werken K, et al. Meta-analysis of resting metabolic rate in formerly obese subjects. Am J Clin Nutr. 1999 Jun;69(6):1117-22.

[21] Dulloo AG, Jacquet J, Girardier L. Poststarvation hyperphagia and body fat overshooting in humans: a role for feedback signals from lean and fat tissues. Am J Clin Nutr. 1997;65:717–723.

[22]Speakman JR, Levitsky DA, Allison DB, et al. Set points, settling points and some alternative models: theoretical options to understand how genes and environments combine to regulate body adiposity. Dis Model Mech. 2011 Nov;4(6):733-45. 

[23] Schwartz MW, Woods SC, Seeley RJ, et al. Is the energy homeostasis system inherently biased toward weight gain? Diabetes. 2003 Feb;52(2):232-8. 

[24] Corbett SW, Stern JS, Keesey RE. Energy expenditure in rats with diet-induced obesity. Am J Clin Nutr. 1986 Aug;44(2):173-80.

[25] Rolls B.J., Rowe E.A., Turner R.C. Persistent obesity in rats following a period of consumption of a mixed high energy diet. J Physiol. 1980 Jan;298:415-27. 

[26]Faust I.M., Johnson P.R., Stern J.S., Hirsch J. Diet-induced adipocyte number increase in adult rats: a new model of obesity. Am. J. Physiol., 235 (1978), pp. E279-E286

[27] Dykes J et al. Socioeconomic gradient in body size and obesity among women: the role of dietary restraint, disinhibition and hunger in the Whitehall II study. International Journal of Obesity 2004 Feb,:262-68.

[28] Poskitt EM. Countries in transition: underweight to obesity non-stop? Ann Trop Paediatr. 2009 Mar;29(1):1-11.

[29] Gary Taubes. 2011. Why we get fat. New York: Anchor Books, Pages 31-40.

[30]Garvey WT. Is Obesity or Adiposity-Based Chronic Disease Curable: The Set Point Theory, the Environment, and Second-Generation Medications. Endocr Pract. 2022 Feb;28(2):214-222. 

[31]Montani JP, Schutz Y, Dulloo AG. Dieting and weight cycling as risk factors for cardiometabolic diseases: who is really at risk? Obes Rev. 2015 Feb;16 Suppl 1:7-18.
      

According to George A. Bray (as of 2020, an emeritus professor at Pennington Biomedical Research Center), until the 1960’s, obesity was viewed as a "lack of will power," and many people thought, and some said "if only these patients would push themselves away from the table, they would not have this problem." 

With this view of obesity, he reflects that the turning point for obesity being accepted as a bona fide area of academic interest were the studies on overfeeding. Overfeeding studies began to provide valuable insights into the biology of obesity. For Doctor Bray, who was a postdoctoral fellow at the New England Medical Center Hospital in Boston at the time, the excitement that was generated when the Vermont overfeeding studies were first presented in 1968 was unforgettable[1].

This was the case with the overfeeding experiments conducted by Doctor Ethan Sims in the late 1960’s. Until then, it was commonly believed that, "overeating obviously leads to obesity," so few such experiments had been conducted.

According to Dr. Jason Fung, the author of “The Obesity Code,” Dr. Sims recruited lean students at the nearby University of Vermont and encouraged them to eat a lot to gain weight. However, despite what both he and the students had expected, the students did not become obese. 

Over two hundred days on this overfeeding regimen, twenty inmates gained an average of twenty to twenty-five pounds. (About 10 kg.) However, once the experiment ended and their caloric intake returned to normal, the men had difficulty maintaining the weight gain, and most shed all the weight they had gained relatively easily. The exceptions were two inmates who struggled to lose that weight[3].

At the time, Dr. Bray was allowed to participate as a co-researcher in Dr. Sims' experiment to examine the metabolic changes occurring in adipose tissue during the weight gain that followed overfeeding. 

Later, in 1972, he conducted his own overeating experiment, using himself as a guinea pig. Initially, he tried to double what he usually ate at each meal, but he couldn't finish, so he switched to energy-dense foods, such as ice cream.

Dr.Bray states that this rapid return to normal weight contrasts with the difficulties people with spontaneous obesity have in losing weight, and the even more difficult task of a maintaining a lower weight. Many who develop obesity over years suffer from a different kind of pain than those of us who acutely gain weight by overfeeding. For them, the obesity “slips up” on them and once present, is difficult to reverse.

The history of overfeeding and underfeeding trials and other lines of evidence clearly show that obesity prevention and treatment cannot simply rely on the advice to "eat less and exercise more." [1]

Alex Leaf (Western States University) and Jose Antonio (Nova Southeastern University) reviewed overfeeding studies conducted up to 2017 that evaluated various combinations of macronutrient overfeeding and its effects on body composition. 

They found twenty-five overfeeding studies that reported changes in fat mass (FM) and fat-free mass (FFM), in addition to changes in body weight. The study durations ranged from nine to one hundred days, and all but four were conducted in sedentary populations[4]. Notably, the objectives of each study varied, and not all mentioned weight loss following the end of the experiments.

To give a few examples, a study on identical twins was published in 1990.

■Bouchard (Laval University, Canada) et. al. recruited twelve pairs of young adult male identical twins (twenty-four individuals) with no exercise habits. Each participant's energy requirements were measured during a two-week base-line period, and after that, they were overfed by 1000 kcal per day (comprising 15% protein, 35% fat, and 50% carbohydrates), six days per week, for a total of eighty-four days during a one hundred-day period. The men were housed in a closed section of a university dormitory, and were under supervision by staff all day. 

■Conford (University of Michigan) et. al. conducted a study in 2012 involving nine healthy, non-obese adults (seven men and two women). The participants were admitted to the hospital for two weeks, during which time they ate 4000 kcals per day (comprising 15% protein, 35% fat, and 50% carbohydrates). Their energy requirements were determined during a one-week baseline period before the start of the experiment. In addition to three main meals, they had four snacks each day. The average weight gain was 2.1 kg, of which 67 % was fat mass (FM).[6]

The summary of this review indicates that overfeeding healthy, sedentary adults with a diet moderately high in both carbohydrates and fats (35-50% energy intake each) and low in protein (11-15%) primarily results in a gain in fat mass (FM), which accounts for 60-70 % of the weight gain. Additionally, the increase in fat-free mass (FFM) may be due to an increase in body water content rather than skeletal muscle tissue. In contrast, diets with significantly increased protein intake showed favorable changes in body composition, even with increased energy intake[4]. 

Why did the participant’s weight rapidly return to normal over the ensuing weeks when they stopped overeating?

According to Dr. Bray, one of the striking findings in this Vermont study was that to maintain the weight they gained after overfeeding, they required more energy per unit surface area than before weight gain. When Dr. Bray moved to the University of California in 1970, his new lab began operating to explore his hypothesis about why extra energy was required to maintain the increased weight[1].

■Leibel (Rockefeller University) et. al. conducted a study in 1995 involving eighteen obese (BMI of 28 or higher) subjects (Group A) and twenty-three subjects who had never been obese (Group B).

They measured changes in energy expenditure under three conditions: at their usual body weight, after losing more than 10 percent of their body weight by underfeeding, and after gaining 10 percent of their body weight by overfeeding.

The study concluded that maintenance of a reduced weight or elevated body weight is associated with compensatory changes in energy expenditure, which resist maintaining the altered body weight and function to restore the original weight. This suggests that the long-term effectiveness of obesity treatment through caloric reduction may be limited[7]. 

As Dr. Bray mentioned, I also believe that weight gain from temporary excessive caloric intake is due to body mechanisms entirely different from those underlying fundamental obesity. If compensatory metabolic mechanisms resist changes in body weight, why do some people continue to gain weight?

As I have repeatedly mentioned through this blog, the difference between people who are overweight and lean can be explained by the difference in set-point for body weight. (One's set-point weight goes up through intestinal starvation.) 

For example, suppose a person who normally weighs a stable sixty kg  is temporarily overfed and reaches sixty-three kg. 

Today, we are sometimes said to be living in an "obesogenic environment" that promotes obesity, but that does not necessarily mean consuming high-calorie foods or living sedentary lifestyles. As some researchers have already mentioned, calorie counting is clearly of little significance. Changes in caloric intake only lead to temporary weight gain or loss. 

     
Rader, the "obesogenic environment" in my opinion is related to foods that are overly digestible foods (refined carbohydrates, fast food, processed foods, etc.) and an imbalanced diet (lack of vegetables, etc.). When these factors overlap with some other conditions such as skipping breakfast or eating late dinners, intestinal starvation is more likely to be induced.

Of course, researchers will say that in order to gain weight, more energy must be taken into the body than before. For more on why intestinal starvation leads to greater energy intake and weight gain, please refer to the article below.

[Related article]　 Gaining Weight by Intestinal Starvation; What Does It Mean?

<References>

[1]Bray GA. The pain of weight gain: self-experimentation with overfeeding. Am J Clin Nutr. 2020 Jan 1;111(1):17-20. 

[2] Fung J, The Obesity Code, Greystone books, 2016, P114-116.

[3] Jou C. The biology and genetics of obesity--a century of inquiries. N Engl J Med. 2014 May 15;370(20):1874-7.  

[4] Leaf A, Antonio J. The Effects of Overfeeding on Body Composition: The Role of Macronutrient Composition. Int J Exerc Sci. 2017 Dec 1;10(8):1275-1296. 

[5] Bouchard C et al. The response to long-term overfeeding in identical twins. N Engl J Med. 1990 May 24;322(21):1477-82. 

[6] Cornford AS et al. Rapid development of systemic insulin resistance with overeating is not accompanied by robust changes in skeletal muscle glucose and lipid metabolism. Appl Physiol Nutr Metab. 2013 May;38(5):512-9. 

[7] Leibel RL et al. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995 Mar 9;332(10):621-8.