Tag Archives: cause of obesity

Ludwig Versus Guyenet: Why Are We Fat?

Neither Ludwig nor Guyenet

Neither Ludwig nor Guyenet

Dr. David Ludwig and Dr. Stephan Guyenet recently debated why we get fat. Ludwig favors the Carbohydrate-Insulin-Obesity Theory. Guyenet thinks leptin plays a central role although it’s by no means the only piece of the puzzle. It’s a gross oversimplification, but let’s just call it the Leptin Theory.

Guyenet published a critique of Ludwig’s proposition, then Ludwig released a response. This would be a good time to click and read the Ludwig response link unless you’re already bored.

Guyenet’s explanation of overweight and obesity “acknowledges the fact that body weight is regulated, but the regulation happens in the brain, in response to signals from the body that indicate its energy status. Chief among these signals is the hormone leptin, but many others play a role (insulin, ghrelin, glucagon, CCK, GLP-1, glucose, amino acids, etc.).”

Rather than paraphrase Guyenet’s response to Ludwig’s response, I’m just going to quote the most pertinent parts:

Here is a simplified schematic overview of how the system works, from a 2012 review paper I wrote with my scientific mentor Mike Schwartz, titled “Regulation of food intake, energy balance, and body fat mass” (1). This figure summarizes more than a century of research in our field:


(graphic from Dr. Guyenet’s blog)

Here’s the gist of it: there are negative feedback loops between the brain and fat tissue, and between the brain and the gut. These are what regulate body fatness and appetite. The primary known feedback signal that regulates body fatness is leptin– a fact that has remained scientifically unchallenged since shortly after its identification in 1994. Insulin plays a role as well, acting directly on the brain in a manner similar to leptin, although much less powerfully. As you can see, this model doesn’t resemble the CICO model– or the insulin model.

Regulation happens principally as a result of the brain changing the number of calories entering and leaving the body (in humans, mostly entering)– so the much-maligned calorie maintains a central role in the process. Even though calories aren’t the first link in the causal chain, they are nevertheless a critical link.

Most people in my field also believe that calorie intake is determined both by hunger (homeostatic eating), and factors other than hunger (non-homeostatic eating). I agree with them.

Why does it matter which of the theories, or some other hypothesis, is correct? Well, if we want to cure or reverse the overweight and obesity epidemic, it might be helpful if we know the cause. Then we address the cause directly. For example, if I have a patient with fever, my treatment plan depends on whether the fever is caused by cancer, an overactive thyroid, adverse drug effect, environmental heat exposure, a broken thermometer, or infection.

Steve Parker, M.D.

Steve Parker MD, Advanced Mediterranean Diet

Two diet books in one

Dr. Eades: Why We Got Fat

Dr. Michael Eades of Protein Power fame thinks he knows why we’ve gotten fat starting 35 years ago (at least in the U.S.:

Along with carbohydrates, vegetable oils have increased dramatically in the typical American diet. Over the same time period, we’ve all started eating away from home more and more, so that we’ve lost control of exactly what kinds of fats we’ve been eating.

Click the link for the details of his hypothesis, which involves the effects of various dietary fats and carbohydrates on intracellular energy metabolism and insulin resistance.

Steve Parker, M.D.

Steve Parker MD, Advanced Mediterranean Diet

Two diet books in one

It’s Your Mother’s Fault You’re Fat

Or so suggests an article at Obesity Reviews. Women who gained excessive weight while pregnant had children prone to obesity both early and later in life. The opposite applies to women who didn’t gain enough weight during pregnancy.


Do We Really Know the Cause of Overweight and Obesity?

So easy to over-eat!

So easy to over-eat!

Isn’t it just ’cause we eat too much and exercise too little due to lack of discipline and willpower?

Science writer David Berreby has an article at Aeon suggesting it’s way more complicated than that. Even if we do eat too much, why do we? Some quotes:

And so we appear to have a public consensus that excess body weight (defined as a Body Mass Index of 25 or above) and obesity (BMI of 30 or above) are consequences of individual choice. It is undoubtedly true that societies are spending vast amounts of time and money on this idea. It is also true that the masters of the universe in business and government seem attracted to it, perhaps because stern self-discipline is how many of them attained their status. What we don’t know is whether the theory is actually correct.


As Richard L Atkinson, Emeritus Professor of Medicine and Nutritional Sciences at the University of Wisconsin and editor of the International Journal of Obesity, put it in 2005: ‘The previous belief of many lay people and health professionals that obesity is simply the result of a lack of willpower and an inability to discipline eating habits is no longer defensible.’

Like liver, skeletal muscle, and brain, our body fat is a tissue that is carefully regulated by genes, hormones, enzymes, etc., which I’ll lump together as “metabolism.” Regulatory metabolic processes for liver, muscle, and brain will be different from each other and from fat tissue. Some processes aid fat storage, others lead to fat breakdown and weight loss.

Mr. Berreby discusses various trendy factors that may directly alter fat tissue metabolic processes, leading to overweight and obesity. Here’s his list:

  • lack of sleep
  • viruses (e.g., Ad-36)
  • stress
  • bacteria (e.g., Methanobrevibacter smithii in the large intestine)
  • industrial chemical contaminants (e.g., BPA, heavy metals, detergents, sunscreen, fire retardants, cosmetics)
  • electrification (e.g., too much light exposure, especially at night)
  • heat and air conditioning
  • undernutrition (“starvation”) during pregnancy: the children hatched are more likely to be overweight or obese as adults
  • intergenerational influence (epigenetic)

Read all about it.

Steve Parker, M.D.