Insulin regulates blood glucose primarily by two mechanisms:
Suppressing glucose production by the liver
Enhancing glucose uptake by other tissues, particularly muscle and liver
Since the cells contained in liver, muscle and other tissues respond directly to insulin stimulation, most people don't think about the role of the brain in this process. An interesting paper just published in Diabetes reminds us of the central role of the brain in glucose metabolism as well as body fat regulation (1). Investigators showed that by inhibiting insulin signaling in the brains of mice, they could diminish insulin's ability to suppress liver glucose production by 20%, and its ability to promote glucose uptake by muscle tissue by 59%. In other words, the majority of insulin's ability to cause muscle to take up glucose is mediated by its effect on the brain.
Last Friday, it was my pleasure to attended and present at the Harvard Food Law Society's TEDx conference, Forum on Food Policy. I had never been to Cambridge or Boston before, and I was struck by how European they feel compared to Seattle. The conference was a great success, thanks to the dedicated efforts of the Food Law Society's presidents Nate Rosenberg, Krista DeBoer, and many other volunteers.
Dr. Robert Lustig gave a keynote address on Thursday evening, which I unfortunately wasn't able to attend due to my flight schedule. From what I heard, he focused on practical solutions for reducing national sugar consumption, such as instituting a sugar tax. Dr. Lustig was a major presence at the conference, and perhaps partially due to his efforts, sugar was a central focus throughout the day. Nearly everyone agrees that added sugar is harmful to the nation's health at current intakes, so the question kept coming up "how long is it going to take us to do something about it?" As Dr. David Ludwig said, "...the obesity epidemic can be viewed as a disease of technology with a simple, but politically difficult solution".
Each week, I'm receiving more e-mails and comments from people who are successfully losing fat by eating simple (low reward) food, similar to what I described here. In some cases, people are breaking through fat loss plateaus that they had reached on conventional low-carbohydrate, low-fat or paleo diets. This concept can be applied to any type of diet, and I believe it is an important characteristic of ancestral food patterns.
At the Ancestral Health Symposium, I met two Whole Health Source readers, Aravind Balasubramanian and Kamal Patel, who were interested in trying a simple diet to lose fat and improve their health. In addition, they wanted to break free of certain other high-reward activities in their lives that they felt were not constructive. They recently embarked on an 8-week low-reward diet and lifestyle to test the effectiveness of the concepts. Both of them had previously achieved a stable (in Aravind's case, reduced) weight on a paleo-ish diet prior to this experiment, but they still carried more fat than they wanted to. They offered to write about their experience for WHS, and I thought other readers might find it informative. Their story is below, followed by a few of my comments.
In this post, I'll explore whether or not the scientific evidence is consistent with the predictions of the food reward hypothesis, as outlined in the last post.
Before diving in, I'd like to address the critique that the food reward concept is a tautology or relies on circular reasoning (or is not testable/falsifiable). This critique has no logical basis.The reward and palatability value of a food is not defined by its effect on energy intake or body fatness. In the research setting, food reward is measured by the ability of food or food-related stimuli to reinforce or motivate behavior (e.g., 1). In humans, palatability is measured by having a person taste a food and rate its pleasantness in a standardized, quantifiable manner, or sometimes by looking at brain activity by fMRI or related techniques (2). In rodents, it is measured by observing stereotyped facial responses to palatable and unpalatable foods, which are similar to those seen in human infants. It is not a tautology or circular reasoning to say that the reinforcing value or pleasantness of food influences food intake and body fatness. These are quantifiable concepts and as I will explain, their relationship with food intake and body fatness can be, and already has been, tested in a controlled manner.
1. Increasing the reward/palatability value of the diet should cause fat gain in animals and humans
When you want to investigate something using the scientific method, first you create a model that you hope describes a natural phenomenon-- this is called a hypothesis. Then you go about testing that model against reality, under controlled conditions, to see if it has any predictive power. There is rarely a single experiment, or single study, that can demonstrate that a hypothesis is correct. Most important hypotheses require many mutually buttressing lines of evidence from multiple research groups before they're widely accepted. Although it's not necessary, understanding the mechanism by which an effect occurs, and having that mechanism be consistent with the hypothesis, adds substantially to the case.
With that in mind, this post will go into greater detail on the evidence supporting food reward and palatability as major factors in the regulation of food intake and body fatness. There is a large amount of supportive evidence at this point, which is rapidly expanding due to the efforts of many brilliant researchers, however for the sake of clarity and brevity, so far I've only given a "tip of the iceberg" view of it. But there are two types of people who want more detail: (1) the skeptics, and (2) scientifically inclined people who want mechanism. This post is for them. It will get technical at times, as there is no other way to convey the material effectively.