The First Law of Thermodynamics: It is the Foundation for the Two Competing Theories about What Makes Us Fat and How We Can Lose Weight

The first law of thermodynamics, also known as the Law of Energy Conservation, tells us that energy contained in a system must equal the energy coming into it minus the energy going out of it. This is a common sense idea. Any theory that seeks to explain why we get fat and how can we lose weight must ultimately derive from this principle, which is often summarized like this:

CHANGES IN ENERGY STORED IN THE BODY = CALORIES IN - CALORIES OUT

Here is a summary of the two different obesity theories that follow logically from the first law of thermodynamics:

I. Caloric Balance Hypothesis

CHANGES IN ENERGY STORED <= CALORIES IN - CALORIES OUT

Caloric Balance is the theory everyone is taught in school. It assumes that the right side of the equation (the part that deals with Calories In and Calories Out) is "in charge." Raise Calories In (overeat) and/or lower Calories Out (be inactive), and the right side of the equation will get bigger. This forces the left side of the equation to also get bigger to compensate. Hence, it tells us that overeating and inactivity will lead to the storage of excess energy in the body, presumably as fat. Conversely, lower Calories In (eat less) and/or raise Calories Out (exercise more), and the right side of the equation gets smaller. Hence, the left side also must shrink. Thus, eating less and exercising more should lead to weight loss.

II. Lipophilia Hypothesis

CHANGES IN ENERGY STORED => CALORIES IN - CALORIES OUT

This alternative theory was developed in Europe in the 1930s and 1940s. It fell out of fashion after World War II, possibly because it was developed in Germany. It has lain essentially dormant since then, but it was never disproven. Science journalist Gary Taubes recently resurrected Lipophilia in his book, Good Calories Bad Calories. The main idea is that left side of the equation -- not the right side -- is "in charge." In other words, changes in the body's energy stores cause changes in caloric balance. This may sound confusing at first. What it means is that, when some underlying problem messes up our fat tissue and causes it to get bigger, this will then cause us to take in more calories and/or burn fewer calories. When that underlying problem is fixed, the fat tissue will shrink, and this will then cause us to eat fewer calories and/or burn more calories.

Caloric Balance and Lipophilia are both plausible interpretations of the first law of thermodynamics. Both make testable, falsifiable predictions about the real world. And it is pretty likely that only one theory can be correct. So which is it? And how can we tell?

Which Theory is Right: Caloric Balance or Lipophilia?


Do excess calories make us fat? Or do problems in our fat tissue (driven, for instance, by excess insulin secretion) make us fat?

Comparing scientific hypotheses

According to the principles of science, a governing hypothesis must account for all relevant data, not just some of it. This point is crucial. To learn more about how truly rigorous scientific testing should be done, click here. And here is a wonderful essay by Karl Popper on the subject.

Here is our own take on guidelines for comparing these two theories.

Below we compare 11 key predictions made by these two theories derived from the first law of thermodynamics. Click on any link to read more:

Phenomenon Caloric Balance Explanation Lipophilia Explanation
1. Weight Gain Over eating and inactivity--i.e.failed calorie counting--cause us to get fat. Overeating and inactivity are consequences of getting fat.
2. Weight Loss Appetite control and increased activity--i.e. being a good calorie calculator--cause us to lose fat. Appetite control and increased activity are consequences of losing fat.
3. Weight Maintenance To maintain a constant weight over time, one must consciously regulate calories in/calories out. Unconscious homeostatic mechanisms maintain our weight over time, just like they maintain other aspects of the interior milieu, like body temperature.
4. Calorie is a Calorie? The body is a simple machine: a calorie is a calorie. All calories are not equal. The second law of thermodynamics suggests that the body is a complex machine.
5. Obesity Epidemic An epidemic of overeating and inactivity has caused the obesity epidemic. The switch to a low fat/high carb diet has caused the obesity epidemic.
6. Diseases of Civilization Says nothing about why obesity associates with diseases of civilization like diabetes, heart disease, stroke, Alzheimer’s disease, malnutrition and gout. Obesity associates with diseases like diabetes, heart disease, stroke, Alzheimer's disease, malnutrition, and gout because they all stem from a common cause: chronic hyperinsulinemia.
7. Low Carb Diets Carb restricted diets and other measures taken to improve blood insulin levels only lead to weight loss if calorie counting leads to calorie restriction. The low carb diet and other measures taken to improve blood insulin levels can lead to weight loss even when calories are unrestricted.
8. Role of Behavior vs. Role of Physiology in Obesity Obesity is a psychological problem that can be fixed by being a better calorie calculator. Obesity is a physiological problem that can often be fixed simply by a low carb diet.
9. What is Our Fat Tissue The calorie calculator theory says absolutely nothing about how, why, when, and where excess calories 'turn into' fat and nothing about why some people get fat while others don’t. Provides a very specific explanation of how, why, when, and where fat accumulates as well as why some people get fat and others don't.
10. Unexplained Weight Changes People who gain/lose fat as the result of drugs, genetics, diseases, brain injuries, natural body development, hormonal or metabolic shifts or other biochemical activity only do so because these factors somehow change their calorie intake/expenditure. Weight changes resulting from medications, genetics, hormonal changes, and so forth must be caused by indirect changes to fat tissue metabolism.
11. Public Conviction that Calories Count Health authorities almost unanimously support the calorie calculator theory because the evidence supports it and/or because competing hypotheses, like Lipophilia, have been disproven. It is the only correct way to interpret the first law of thermodynamics. Health authorities almost unanimously support the calorie calculator theory only because they are unaware that the Lipophilia Hypothesis even exists and because they have, by and large, ignored the science supporting the low carb diet and ignored the possibility that the first law of thermodynamics could support an alternative theory.

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