Good insulin, bad insulin: Its role in obesity?

Gary Taubes makes insulin out to be a bad guy. In his latest article in Newsweek Magazine commenting on HBO's Weight of the Nation documentary, he once again challenges energy balance (energy intake versus energy expended) as a paradigm for understanding obesity. The author of Good Calories, Bad Calories offers an alternative theory: refined sugars and grains trigger insulin, which leads to fat accumulation. He also doesn't think much of physical activity as playing a "meaningful role in keeping off the pounds."

Is Taubes right? Not according to Jim Hill, Ph.D., a professor of pediatrics and medicine at the University of Colorado School of Medicine, Denver. Hill is the cofounder of the National Weight Control Registry, a registry of individuals who've succeeded in maintaining weight loss over time. He is also the co-founder of America on the Move, a national weight-gain prevention initiative.

At a session at Experimental Biology, Hill said that the the "energy-in energy-out" framework continues to dominate as correct in current scientific literature on obesity. When asked whether or not the rise of obesity epidemic is related to diet or physical activity, Hill simply responds, "Yes." That is because studies have shown that either restriction of calories or greater physical activity can lead to weight loss.

Then, what's wrong with Taubes's insulin hypothesis? First, it's important to point out that insulin is also a good guy. As kinesiologist John Ivy, Ph.D., of the University of Texas at Austin, pointed out to me a few years ago, insulin is too often misunderstood. The unfortunate consequence can be a detriment of muscle and strength. Ivy's own research is on muscle insulin resistance and how it is reduced with exercise.

Insulin's role is more clearly explained in Ivy's book The Future of Sports Nutrition: Nutrient Timing. He writes that, yes, insulin is a promoter of fat synthesis. But it is also a crucial hormone for promoting protein synthesis, reducing protein degradation (including suppressing cortisol, which can be catabolic in nature), and promoting glucose uptake and glycogen storage in muscle. Insulin, notably, also suppresses appetite.

According to Ivy, the most important factor involved in whether or not insulin promotes fat storage, carbohydrate storage, or protein synthesis is the "individual's body state." For example, under conditions where insulin sensitivity heightened in fat cells (a sedentary lifestyle), there will be more promotion of fat storage. On the other hand, after physical activity, when muscle cells are more insulin sensitive, insulin will promote glycogen and protein synthesis.

Perhaps where Taubes goes wrong is in failing to realize the role of muscle in body metabolism. It wouldn't be the first time. As I've discussed before in a post about the work of another kinesiologist, Stuart Phillips, Ph.D., of McMaster University, skeletal muscle is often forgotten in discussions of obesity. However, as Phillips affirms, skeletal muscle is a highly metabolically active tissue, consuming a great deal of energy as a primary site for glycogen storage and the largest site for fat burning. Skeletal muscle mass also helps determine metabolic rate.

Taubes, in this latest article, also fails to mention that carbohydrate is not the only macronutrient that stimulates insulin. Protein stimulates insulin too; in fact, it's the branched-chain amino acids (leucine, isoleucine, valine) that trigger the insulin release -- these same amino acids are also the key players in triggering protein synthesis, which is explained in part by their effects on insulin.

Ivy explains that insulin has earned the title "anabolic regulator of muscle," meaning it's the most important hormone to increase muscle and strength. Yet, by Taubes's judgment, insulin release should be avoided as much as possible. Taken to its logical conclusion, Taubes's mindset means that one should eat less carbohydrate and protein per day, and eat plenty more fat -- along with the dismissal of exercise as being important, that's the perfect recipe for gradual muscle degradation and (what?) insulin resistance, hyperglycemia, and hyperinsulinemia!

Is there something really wrong with "eat less, move more"? After all, this "tired advice" as Taubes calls it has largely failed in producing results in the United States. There still exists an obesity epidemic and it's getting worse. Is there another alternative theory to energy balance? Hill says energy balance still stands, although he acknowledges "eat less, move more" is too simplistic as advice. He offers his own new paradigm, which largely represents what other nutrition scientists have concluded including the American Society for Nutrition (see my report here). It's that "diet and physical activity interact." And how they interact may explain how the body regulates -- with a sort of "settling point," according to Hill -- balance of energy, energy stores, glucose, and temperature.

Looking at the problem from historical standpoint, Hill reminds, we no longer have to hunt or travel long distances to gather food anymore. We no longer have to farm to produce our food. Now, it's all about heading to the supermarket, filling our carts, and sitting in some form or another for the rest of the day. Our environment has changed. What's the solution to an obesity epidemic? Hill suggests in taking "small steps" for changing our environment back; this means continuing with "eat less, move more," and finding any opportunity to bring reduced-calorie eating, walking, and other physical activities back into lifestyles.

Another recommendation comes from Ivy and Phillips, which is to make greater use of the "anabolic regulator of muscle" and focus on muscle maintenance and growth through regular physical activity. They also encourage balanced eating with healthy portions of quality protein, carbohydrates, and fats. Yes, carbohydrate is important for endurance and maximal recovery of glycogen stores.

Resistance training is primary for muscle building; aerobic exercise also helps in depletion of glycogen stores. Both forms of physical activity make muscles more insulin sensitive, cause greater uptake of glucose into muscles, and they also help keep extra calories from heading toward fat stores. Far from Taubes's advice that physical activity is meaningless, these kinesiologists suggest some form of exercise should happen every single day.

To greater understand the role of "nutrient timing" and how carbohydrate and protein relate to exercise, read Ivy's book and see this 2008 position statement from the International Society of Sports Nutrition where Ivy serves as part of the editorial board.

Update: Those of you who've read Good Calories, Bad Calories or Why We Get Fat may also be interested in Yoni Freedhoff's review of the latter over on his "Weighty Matters" blog. I have only read the first book.