Why doesn’t exercise and diet reduce heart disease for diabetics?

That’s a good question after the June 24 issue of the New England Journal of Medicine reported on the failure of long-term diet and exercise to reduce heart disease in diabetics1. It had been known from earlier and shorter studies that diet and exercise in diabetics appeared to generate a decreased risk of cardiovascular disease. This is important since heart disease remains the number-one killer of Americans, and people with diabetes are two to four times more likely to develop heart disease. Since diabetes is becoming epidemic, this would suggest that heart disease should soon begin to escalate. But for exercise and diet have any benefits in any condition, they have to been continued forever. That is the motivation for this 13-year study that started with the best of intentions. However, last year the study was terminated at 10 years since it was clear that there were no cardiovascular benefits. Now that the study details have been published, it is clear why it failed.

First, all of the success of diet and exercise started to evaporate after the first year. Remember, the people who enter these studies are highly motivated with a terrible future awaiting them. So why would they seemingly throw away all the initial benefits of weight loss and reduction of blood sugar? Part of the reason can be explained by why most diet program fail: Willpower can only take you so far if your hormones are working against you. The end result is you are constantly hungry and always tired.

The amount of calories the subjects of this study consumed was low (between 1,200 and 1,800 calories per day), but the diet was a high-carbohydrate diet (that induces low blood sugar due to hyperinsulinemia). The diet was coupled with lots of exercise (that also lowers blood sugar). This is an almost surefire prescription to be constantly hungry and tired. As a result, compliance wanes.

On the other hand, if you are never hungry, then compliance is better. That was the case with another 13-year study of diabetic patients who had gastric bypass surgery. For these patients, there was a significant reduction in cardiovascular events2. The reason is probably hormonal. If you lose weight by diet and exercise, your levels of the hunger hormone ghrelin increases with no change in the levels of your satiety hormone, PYY. Just the opposite happens with gastric bypass surgery. Ghrelin doesn’t change, but PYY increases3. The result is that you are not hungry, and therefor your lifestyle compliance improves.

Of course, giving every diabetic gastric bypass surgery makes little sense. Giving them new, more powerful diabetic drugs with equally powerful side effects (like heart attacks) also makes no sense.

There may be third way: Functional foods that can increase PYY levels. But these have to be tasty (like pasta and rice) and convenient (only 90 seconds to make) since you have to take them the rest of your life. That’s the project I have been working on for the past six years. These new Zone meals may be the answer, as they appear to reduce hunger without causing fatigue while eating the foods you like to eat. Zone meals are low-tech medicine with potentially high-tech results and are coming soon.

References

  1. Wing RR et al. “Cardiovascular effects of intensive lifestyle intervention in type 2 diabetes.” NEJM DOI:10.1056/NEJMoa 1212914 (2013)
  2. Romeo S et al. “Cardiovascular events after bariatric surgery in obese subjects with type 2 diabetes.” Diabetes Care 35: 3613-2617 (2012)
  3. Olivan B et al. “Effect of weight loss by diet or gastric bypass surgery on peptide YY3-36 (PYY) levels.” Ann Surg 249: 948-953 (2009)
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About Dr. Barry Sears

Dr. Barry Sears is a leading authority on the impact of the diet on hormonal response, genetic expression, and inflammation. A former research scientist at the Boston University School of Medicine and the Massachusetts Institute of Technology, Dr. Sears has dedicated his research efforts over the past 30 years to the study of lipids. He has published more than 30 scientific articles and holds 13 U.S. patents in the areas of intravenous drug delivery systems and hormonal regulation for the treatment of cardiovascular disease. He has also written 13 books, including the New York Times #1 best-seller "The Zone". These books have sold more than 5 million copies in the U.S. and have been translated into 22 different languages.

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