What does insulin resistance have to do with overweight and weight loss?

We observe all the time that some people seem to be able to eat anything and not gain weight, and others eat very little and are heavy.  The calories in/calories out dogma denies that this phenomenon exists, but we all know it does.  At the Packard pediatric weight control program, one of the most difficult things for the children there to handle was the fact that it seemed their peers could eat anything they wanted, including chips, candy, and soda, and be slim.  And they were right.

How is this possible?  How an individual will respond to the typical American diet is dictated by how insulin sensitive or insulin resistant they are.  The typical American diet is high in carbohydrates.  Carbohydrates cause the body to produce insulin to keep blood sugar in a normal range.  (An equal amount of energy consumed as fat causes virtually no change to insulin levels).  Some individuals are sensitive to insulin–they can process a given amount of carbohydrate with relatively little insulin release.  But some are insulin resistant–they require a lot of insulin to process that same amount of carbohydrate.

Insulin is also known in any biology textbook as “the fat storage hormone.”  Can you guess which individual is going to gain weight from the typical American diet?

Relative insulin sensitivity or resistance also explains how an individual is going to respond to different sorts of eating plans designed for weight loss.  The insulin sensitive individual can lose weight on a low fat, low calorie plan or on a low carb plan.  But the insulin resistant individual will find it very hard to lose weight on a low fat, low calorie plan:

“Insulin Resistance and Diet Success

In 2007, Gardner et al published a randomized, controlled trial called the A-to-Z Study involving 4 diets lasting a year given to groups of obese women[43]. At one end of this diet spectrum was the ‘Ornish diet’ which is very high in complex carbs and very low in fat. At the other end was the ‘Atkins diet’ (i.e., low carbohydrate). After 6 months, the women on Atkins had lost significantly more weight, but after 12 months they were still lower but not significantly so. Interestingly, blood pressure and HDL cholesterol were significantly better on low carbohydrate than any of the other diets, and this beneficial effect remained significant out to 12 months. After publishing this initial paper in JAMA, Dr. Gardner went back and examined his data based upon the subjects’ insulin levels before they started dieting. When the women on each diet were divided into three subgroups (tertiles) based on baseline insulin resistance, the results were striking. In the low carbohydrate diet group, weight loss was similar in the most insulin sensitive (11.7 lbs) and insulin resistant (11.9 lbs) women. However weight loss with the high carbohydrate (Ornish) diet was much greater in the insulin sensitive (9.0 lbs) than the insulin resistant (3.3 lbs) women. Thus the most insulin sensitive sub-groups of women experienced a similar weight loss when assigned diets either high (9.0 lbs) or low (11.7 lbs) in carbohydrate In contrast, the sub-groups that were insulin resistant fared very poorly when assigned a diet high in carbohydrate (3.3 lbs lost) compared to a low carbohydrate diet (11.9 lbs). Specifically, those women with insulin resistance lost almost 4-times as much weight when dietary carbohydrates were restricted[44].”

Phinney, Stephen; Volek, Jeff (2011-07-08). The Art and Science of Low Carbohydrate Living: An Expert Guide to Making the Life-Saving Benefits of Carbohydrate Restriction Sustainable and Enjoyable (pp. 85-86). Beyond Obesity LLC. Kindle Edition.

They may lose some, like Juliana did, because a low fat, low calorie plan is almost certainly also a lower carb plan.  But the insulin resistant people are going to be hungrier than the insulin sensitive people on an Ornish-type plan.  Why?  The more insulin, the more the cells get the message to store available energy as fat.  The more that is stored as fat, the less is available to use, and the sooner that person will be hungry again.

I have already taken Dr Dean Ornish to task for publishing a misleading opinion piece in The New York Times blasting low carb eating plans.  He would also do well to pay attention to his patients who cannot comply with his eating plan because of hunger, or don’t lose much weight even if they do comply.   He might learn something.