The Neurobiology of the Obesity Epidemic

I recently read an interesting review paper by Dr. Edmund T. Rolls titled "Taste, olfactory and food texture reward processing in the brain and the control of appetite" that I'll discuss in this post (1). Dr. Rolls is a prolific neuroscience researcher at Oxford who focuses on "the brain mechanisms of perception, memory, emotion and feeding, and thus of perceptual, memory, emotional and appetite disorders." His website is here.

The first half of the paper is technical and discusses some of Dr. Rolls' findings on how specific brain areas process sensory and reward information, and how individual neurons can integrate multiple sensory signals during this process. I recommend reading it if you have the background and interest, but I'm not going to cover it here. The second half of the paper is an attempt to explain the obesity epidemic based on what he knows about the brain and other aspects of human biology.

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Speaking at AHS13

The 2013 Ancestral Health Symposium will be held in Atlanta, GA, August 14-17.  Last year was a great conference, and I look forward to more informative talks and networking.  Tickets go fast, so reserve yours now if you plan to attend!

This year, I'll be speaking on insulin and obesity.  My talk will be titled "Insulin and Obesity: Reconciling Conflicting Evidence".  In this talk, I'll present the evidence for and against the idea that elevated insulin contributes to the development of obesity.  One hypothesis states that elevated insulin contributes to obesity, while the other states that elevated insulin is caused by obesity and does not contribute to it.  Both sides of the debate present evidence that appears compelling, and it often seems like each side is talking past the other rather than trying to incorporate all of the evidence into a larger, more powerful model.

There's a lot evidence that can be brought to bear on this question, but much of it hasn't reached the public yet.  I'll explore a broad swath of evidence from clinical case studies, observational studies, controlled trials, animal research, physiology, and cell biology to test the two competing hypotheses and outline a model that can explain all of the seemingly conflicting data.  Much of this information hasn't appeared on this blog.  My goal is to put together a talk that will be informative to a researcher but also accessible to an informed layperson.

On a separate note, my AHS12 talk "Digestive Health, Inflammation and the Metabolic Syndrome" has not been posted online because the video recording of my talk has mysteriously disappeared.  I think many WHS readers would be interested in the talk, since it covers research on the important and interdependent influence of gut health, inflammation, and psychological stress on the metabolic syndrome (the quintessential modern metabolic disorder).  I'm going to try to find time to make a narrated slideshow so I can post it on YouTube.

Food Variety, Calorie Intake, and Weight Gain

Let's kick off this post with a quote from a 2001 review paper (1):

Increased variety in the food supply may contribute to the development and maintenance of obesity. Thirty-nine studies examining dietary variety, energy intake, and body composition are reviewed. Animal and human studies show that food consumption increases when there is more variety in a meal or diet and that greater dietary variety is associated with increased body weight and fat.

This may seem counterintuitive, since variety in the diet is generally seen as a good thing. In some ways, it is a good thing, however in this post we'll see that it can have a downside.
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Food Reward Friday

This week's lucky "winner"... ice cream!!

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Book Review: Salt, Sugar, Fat

Michael Moss is a Pulitzer prize-winning journalist who has made a career writing about the US food system. In his latest book, Salt, Sugar, Fat: How the Food Giants Hooked Us, he attempts to explain how the processed food industry has been so successful at increasing its control over US "stomach share". Although the book doesn't focus on the obesity epidemic, the relevance is obvious. Salt, Sugar, Fat is required reading for anyone who wants to understand why obesity is becoming more common in the US and throughout the world.

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Food Reward Friday

This week's lucky "winner"... energy bars!

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Thoughts on Obesity, Part I

From the US Centers for Disease Control website:

Since the mid-seventies, the prevalence of overweight and obesity has increased sharply for both adults and children. Data from two NHANES surveys show that among adults aged 20�74 years the prevalence of obesity increased from 15.0% (in the 1976�1980 survey) to 32.9% (in the 2003�2004 survey).

In hunter-gatherer and some semi-agricultural societies, obesity is rare. In most, it's nonexistent. Wild animals typically do not accumulate enough fat to interfere with vigorous exercise, and when they do, it's because they're about to hibernate or migrate. Wild animals also tend to have similar amounts of body fat between individuals (at a given age and sex), unlike industrialized humans. This makes me think that obesity is an unnatural effect of our current lifestyle. Whatever the cause, it's getting progressively more common.

According to certain nutrition experts, we know exactly what causes overweight. It's a character flaw known as overeating. Calories in, calories out. And the cure is to eat less. The problem is, this treatment has a poor record of efficacy.

Restricting calories is also fraught with problems. Each person's metabolism has a preference for a specific body composition within the context of a particular lifestyle. If total calories are restricted without changing diet composition, the body reacts vigorously to maintain homeostasis. Energy expenditure is reduced; muscle and organ mass diminish. The psychological effects are particularly bad, as anyone can tell you who has been on a low-calorie diet. In 1944, Ancel Keys undertook a calorie restriction trial in conscientious objector "volunteers" in Minnesota. They remained on a 1,570-calorie diet that was low in fat and protein and high in carbohydrate, for 24 weeks. Hardly a draconian calorie count. Here's a quote from the study:

As starvation progressed, fewer and fewer things could stimulate the men to overt action. They described their increasing weakness, loss of ambition, narrowing of interests, depression, irritability, and loss of libido as a pattern characteristic of "growing old".

Some of the men ended up suffering from neurosis and borderline psychosis before the end of the study, one culminating in self-mutilation. This is what we're being prescribed for weight loss?

There are some diet trends that have associated with rising obesity in the US. Per capita calorie consumption has increased. This increase is due to a higher consumption of carbohydrate. Total protein and fat consumption have been almost identical for the past 30 years. This period also saw increases in the consumption of unsaturated vegetable oils, hydrogenated vegetable oils and high-fructose corn syrup. It's hard to say from this association which of these factors (if any) has caused us to gain weight in the last 30 years, but it certainly isn't total fat or protein. Fortunately, we have other clues.