<Note 1>

In 1878, German nutritionist Max Rubner crafted what he called the "isodynamic law". The law claims that the basis of nutrition is the exchange of energy, and was applied to the study of obesity in the early 1900s by Carl von Noorden. (Wikipedia [A calorie is a calorie])
       

References:
[1] Jason Fung. The Obesity Code. Greystone books. 2016. Page 30.

[2] Rob Dunn. Science Reveals Why Calorie Counts Are All Wrong. 2013.

[3] Japan Food Research Laboratories. The Energy Content of Food. 2003 Jul.

[4] Gary Taubes. Why We Get Fat. 2013. New York: Anchor books. Pages 144-158.

[5]Jason Fung. The Obesity Code. 2016. Pages 100-1.

[6]Jason Fung. The Obesity Code. 2016. Pages 19-20.
        

This time, I would like to discuss three key factors－plus one additional factor－that may contribute to the occurrence of what I call “intestinal starvation."

【Related article】

In addition to these, many other factors may also be indirectly involved in the recent increase in obesity. However, it is not always clear how multiple factors combine to drive weight gain across the population as a whole.

I propose that one possible explanation involves a mechanism I refer to as “intestinal starvation.”

This condition is unlikely to occur due to a single factor alone, but is more likely to arise when the three factors (+1) described below overlap at the same time. For this reason, it may help explain how everyday eating habits and lifestyle patterns—when considered together—can lead to weight gain.

This idea is consistent with the view that consuming low-GI (glycemic index) foods and minimally processed foods help prevent obesity.

It doesn’t depend on the amount of calories you eat, but the quality and balance of food you eat. For example, eating a variety of foods and having a good balance vs a bad balance may lead to gaining weight, even if you eat small amounts.

Eating speed, how well you chew, and how much fluid you drink during meals may also influence this factor.

【Related article】
The Dilution Effect/ Pushing Out Effect of Carbohydrates

Eating Fat/Oil Can be a Deterrent to Gaining Weight (3 Perspectives Regarding Fat)

Many people report gaining weight due to lifestyle changes such as skipping breakfast or eating dinner late at night. Behind this type of weight gain caused by irregular daily routines lies the issue of long gaps between meals—in other words, enduring hunger for extended periods of time.

Eating late at night does not always lead to weight gain by itself. If dinner has to be late, having a small snack in the early evening—such as nuts, milk, or a sandwich—can help prevent intestinal starvation by avoiding prolonged hunger.

Even when eating the same meals, people with strong stomachs and high digestive capacity may be more likely to experience intestinal starvation than those whose digestion is slower. In today’s society, where energy-dense foods are common, the ability to digest protein and fat may have a particularly strong influence on whether intestinal starvation occurs.

On the other hand, people with sensitive stomachs or conditions such as gastroptosis may find it difficult to fully digest all ingested food in the first place.

If genetic factors contribute to obesity, then the secretion of enzymes and hormones that affect digestive capacity and appetite, as well as the sensitivity of their receptors, is likely to play a major role. Of course, these factors can also change due to environmental and lifestyle influences.
      

In addition to the three factors, I added one more important element as “+1,” which can be explained by “continuity.”

What this means is that not only the meal you have just finished, but also your previous meal and the meals before that can influence whether intestinal starvation occurs or not. 

The reason is that the intestines are very long—about 7 to 8 meters in total (with the small intestine alone being about 6 meters)—and it takes, on average, more than ten hours for food to pass through the entire intestinal tract. Because intestinal starvation is judged across the whole intestine (or possibly only the small intestine), it is influenced not only by a single meal, but also by your previous meal and the meals before that.

This is also the flip side of why eating well-balanced meals three times a day is thought to help prevent obesity: it helps ensure that the intestines are continuously exposed to food of adequate quality, reducing the chance that the body interprets the situation as “starvation.” 

From an evolutionary biology perspective, humans and many other animals are thought to have developed mechanisms to cope with intermittent food shortages over long periods of evolution. Because periods of abundant food were limited, the ability to store energy in the liver, skeletal muscles, and adipose tissue was likely favored by natural selection.

From this viewpoint, obesity can be seen not merely as a consequence of overeating, but as a form of adaptive response in which the body stores energy when it perceives a risk of scarcity.

   
The concept of “intestinal starvation” adds a new perspective to the discussion of how our bodies perceive a lack of food, moving beyond the traditional focus on energy intake alone.

【Related articles】
Why Does the Body Perceive That It Is More Starved than in the Past?

(*1) It is unclear whether intestinal starvation is sensed throughout the entire gut or only in the small intestine, which is sometimes referred to as the "second brain."

(*2) Since fats take longer to digest, consuming them every 4 to 5 hours may help prevent the onset of intestinal starvation (e.g., olive oil in the Mediterranean diet). However, during digestion, fats are emulsified into tiny droplets, and once fully digested, they leave no residual material in the gut. In individuals with strong fat-digesting capacity, especially when fats are consumed together with refined carbohydrates, this may not effectively suppress intestinal starvation (e.g., simple hamburgers, potato chips, donuts).

【Related articles】Eating Fat/Oil Can be a Deterrent to Gaining Weight

Even if you consume a large amount of food, a diet composed mostly of refined carbohydrates and other easily digestible items (including certain protein sources and small amounts of fat)—combined with long gaps between meals, such as eating only twice a day—can induce an intestinal starvation state or a condition very close to it.

Even when overall food intake is small, a diet composed mainly of easily digestible foods such as refined carbohydrates and certain protein sources (e.g., ultra-processed foods such as simple burgers or sandwiches, or instant noodles) may still trigger intestinal starvation. 

Due to recent dieting trends, many people try to keep breakfast or lunch light in an effort to lose weight, but this approach may end up being counterproductive in the long run.

In contrast, when you eat a balanced diet including fiber-rich vegetables, and minimally processed foods three times a day, some fraction of undigested material remains in the intestinal tract continuously throughout the day, making it less likely for intestinal starvation to be induced.

Since human genes are unlikely to change dramatically over just a few decades, changes in lifestyle and food environments since the 1970s are thought to have played a major role in the recent global rise in obesity[3].

Strictly speaking, four factors(*3) need to overlap for intestinal starvation to be triggered, which may explain why obesity is more likely to occur at the intersection of multiple factors, including genetic, environmental, and physiological factors.

(*3) The four factors are “what you eat,” duration of hunger, digestive ability, and continuity.

Genetic traits related to intestinal starvation include the secretion capacity and receptor sensitivity of enzymes and hormones that regulate digestion and appetite. In particular, populations or ethnic groups with a greater ability to digest proteins and fats rapidly may be more susceptible to intestinal starvation.

These characteristics may also change as a result of acquired conditions, such as obesity or gastric reduction surgery performed for weight loss.

Since the 1970s, one of the most notable environmental changes, I believe, has not merely been the increase in energy-dense foods, but rather the rise in easily digestible foods resulting from industrialized food production. Examples include refined carbohydrates, certain protein sources, and ultra-processed foods.

In vegetables and grains, the less digestible parts have been removed (e.g., refined grains), and some are now mashed or strained (e.g., mashed potatoes and potage soups). Meat and fish are often minced or ground, making them easier to digest.

<Lifestyle>

Intestinal starvation is related not only to what people eat but also to "how they eat."

Since the 1970s, changes in lifestyle have been accompanied by dramatic shifts in eating habits. In Japan, for example, the traditional rice-based breakfast has gradually been replaced by a Western-style breakfast consisting of toast, coffee, and fried (or boiled) eggs, etc.

    
In addition, many people now tend to eat light breakfasts and lunches, while consuming the majority of their daily calories at dinner. Such eating patterns may promote intestinal starvation, because our intestines are about seven to eight meters long, and all ingested food may be completely digested while traveling through the intestinal tract. 

Intestinal starvation represents an adaptive physiological response related to intestinal processing and hormonal secretion, and may prove that people who eat a balanced diet every day are likely to be less prone to weight gain 

Although intestinal starvation may not be directly associated with the gut microbiota, the types of foods consumed have a significant impact on the intestinal environment.

Individuals who eat a wide variety of foods in a well-balanced manner are less likely to induce intestinal starvation, which may indirectly suggest a relationship that those with a healthier gut microbiota are less susceptible to obesity.

<References>

[1]Flores-Dorantes MT, Díaz-López YE, Gutiérrez-Aguilar R. Environment and Gene Association With Obesity and Their Impact on Neurodegenerative and Neurodevelopmental Diseases. Front Neurosci. 2020 Aug 28;14:863. 

[2]Khan MJ et al. Role of Gut Microbiota in the Aetiology of Obesity: Proposed Mechanisms and Review of the Literature. J Obes. 2016;2016:7353642. 

[3] Jason Fung. The Obesity Code. Greystone Books, 2016, Page 21-2.

In everyday conversation, “gaining weight” is often understood simply as “an increase in body weight (usually body fat)” compared with the past. However, this expression actually encompasses two physiologically distinct processes.

For example, while it is commonly believed that eating high-calorie foods leads to weight gain, understanding phenomena such as post-diet weight rebound—sometimes resulting in greater weight gain than before—requires a physiological perspective.

I believe that because these two distinct processes are often confused, some misinformation about weight loss have gained popularity, leading many people to diet in ways that may be ineffective or misguided.

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The Spread of Dieting May Be Fueling the Rise in Obesity

The first type of “gaining weight” comes from the body’s homeostatic drive to return to its set-point weight (Fig. 1A). 

In many countries, people often talk about “holiday weight gain” or say that high-calorie foods inevitably make them gain weight. Some also claim, “I gain weight as soon as I eat a little more.”

But in most cases, these experiences can be explained by the homeostatic mechanism that pulls body weight back toward its set-point—meaning that the person is simply repeating small cycles of “mini-diets” followed by “mini-rebounds.”

【Related article】
The Set-Point Weight; The Precondition Regarding the Rebound Effect

On the other hand, the second “gaining weight” expression means that one’s set-point weight itself increases (Fig. 1B).

I consider the upward shift in the body’s weight set-point to be driven by a biological adaptive response that occurs when the body perceives a state of starvation—whether due to severe energy deficit from excessive calorie restriction or what I describe in this blog as “intestinal starvation.”

Here, I will focus on the latter: cases in which intestinal starvation appears to raise the set-point. 

I believe this upward shift is not directly related to calories consumed or burned, but rather results from 'intestinal starvation' that can be induced during extended periods of hunger.

【Related article】
Three (+one) Factors to Accelerate “Intestinal Starvation”
    

An increase in the body’s set-point weight can be thought of as the glass itself growing larger in the aforementioned glass-of-water analogy (Fig. 3). This shift may create a fundamental difference between people who tend to gain weight easily and those who remain lean.

In fact, research on set-point theory suggests that, for some individuals, obesity may represent a “natural physiological state” in which energy balance is maintained at a specific higher set-point.

【Related article】
The Increasingly Important "Set-Point" Theory of Body Weight

From this perspective, the common experience of most people regaining weight after dieting can be understood as a homeostatic, weight-preserving mechanism (A) described above.

However, when someone not only regains weight but surpasses their previous maximum, a different mechanism (B) explained here may be at work. This is because during prolonged calorie restriction, the body may perceive itself to be in a state of starvation. 

<References>

[1] 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.