Why Do We Eat? A Neurobiological Perspective. Part II

In the last post, I explained that eating behavior is determined by a variety of factors, including hunger and a number of others that I'll gradually explore as we make our way through the series. These factors are recognized by specialized brain 'modules' and forwarded to a central action selection system in the mesolimbic area (the reward system), which determines if they are collectively sufficient cause for action. If so, they're forwarded to brain systems that directly drive the physical movements involved in seeking and consuming food (motor systems).

The term 'homeostasis' is important in biology. Homeostasis is a process that attempts to keep a particular factor within a certain stable range. The thermostat in your house is an example of a homeostatic system. It reacts to upward or downward changes in a manner that keeps temperature in a comfortable range. The human body also contains a thermostat that keeps internal temperature close to 98.6 F. Many things are homeostatically regulated by the body, and one of them is energy status (how much energy the body has available for use). Homeostasis of large-scale processes in the body is typically regulated by the brain.

We can divide the factors that determine feeding behavior into two categories, homeostatic and non-homeostatic. Homeostatic eating is when food intake is driven by a true energy need, as perceived by the brain. For the most part, this is eating in response to hunger. Non-homeostatic eating is when food intake is driven by factors other than energy need, such as palatability, habitual meal time, and food cues (e.g. you just walked by a vending machine full of Flamin' Hot Cheetos).

We can divide energy homeostasis into two sub-categories: 1) the system that regulates short-term, meal-to-meal calorie intake, and 2) the system that regulates fat mass, the long-term energy reserve of the human body. In this post, I'll give an overview of the process that regulates energy homeostasis on a short-term, meal-to-meal basis.

The Satiety System (Short-Term Energy Homeostasis)


The stomach of an adult human has a capacity of 2-4 liters. In practice, people rarely eat that volume of food. In fact, most of us feel completely stuffed long before we've reached full stomach capacity. Why?

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New Review Paper by Yours Truly: High-Fat Dairy, Obesity, Metabolic Health and Cardiovascular Disease

My colleagues Drs. Mario Kratz, Ton Baars, and I just published a paper in the European Journal of Nutrition titled "The Relationship Between High-Fat Dairy Consumption and Obesity, Cardiovascular, and Metabolic Disease". Mario is a nutrition researcher at the Fred Hutchinson Cancer Research Center here in Seattle, and friend of mine. He's doing some very interesting research on nutrition and health (with an interest in ancestral diets), and I'm confident that we'll be getting some major insights from his research group in the near future. Mario specializes in tightly controlled human feeding trials. Ton is an agricultural scientist at the University of Kassel in Germany, who specializes in the effect of animal husbandry practices (e.g., grass vs. grain feeding) on the nutritional composition of dairy. None of us have any connection to the dairy industry or any other conflicts of interest.

The paper is organized into three sections:

1. A comprehensive review of the observational studies that have examined the relationship between high-fat dairy and/or dairy fat consumption and obesity, metabolic health, diabetes, and cardiovascular disease.
2. A discussion of the possible mechanisms that could underlie the observational findings.
3. Differences between pasture-fed and conventional dairy, and the potential health implications of these differences.

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New Study: Is a Calorie a Calorie?

A new study in JAMA led by Dr. Cara B. Ebbeling and colleagues purports to challenge the idea that all calories are equally fattening (1). Let's have a look. When thinking about the role of calorie intake in body fatness, there are basically three camps:

1. Calories don’t matter at all, only diet composition matters.
2. Calories are the only thing that matters, and diet composition is irrelevant.
3. Calories matter, but diet composition may also play a role.

The first one is an odd position that is not very well populated. The second one has a lot of adherents in the research world, and there’s enough evidence to make a good case for it. It’s represented by the phrase ‘a calorie is a calorie’, i.e. all calories are equally fattening. #1 and #2 are both extreme positions, and as such they get a lot of attention. But the third group, although less vocal, may be closest to the truth.
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