Obesity: Why It is So Important in Diabetes

C. Ronald Kahn, MD, Senior Investigator and Head of the Section on Integrative Physiology and Metabolism, Mary K. Iacocca Professor of Medicine at Harvard Medical School
C. Ronald Kahn, MD, Senior Investigator and Head of the Section on Integrative Physiology and Metabolism, Mary K. Iacocca Professor of Medicine at Harvard Medical School

by C. Ronald Kahn, MD
Joslin Diabetes Center

Everybody has fat.  Even highly trained athletes have at least 10 pounds of fat, and in normal weight men and woman, fat can be as much as 20% of body weight or 20-40 lbs.  When people have more fat than that, we consider them to be overweight or obese. Currently, in the U.S., over 30% of adults are obese and another 30% are overweight. What is even more concerning is that between 25 and 30% of children and adolescents in the U.S. are either overweight or obese too.

Medically we estimate whether body  fat by a measure called BMI (Body Mass Index), which is calculated by a complicated formula involving height (in centimeters) and weight (in kilograms).  BMIs less than 25 are considered normal, between 25 and 30 is overweight, and over 30 is obese.

Why is this important?  When someone becomes obese, they also develop what we call insulin resistance – a condition in which insulin, the major hormone controlling blood sugar, does not work normally.  For people with type 1 diabetes, this means taking more insulin to control blood sugars.  For people prone to developing type 2 diabetes, obesity increases insulin resistance, and this can make the difference between having diabetes and not having diabetes.  It also puts you at risk for many other disorders, including accelerated atherosclerosis, which can lead to heart attacks, and fatty liver disease, which can cause gallstones and liver failure.

That is why losing weight is so important for people with type 2 diabetes, and that is why keeping weight off is so important for those at genetic risk of type 2 diabetes.  People with a strong family history of type 2 diabetes, such as having both parents with the disease, can reduce their risk of diabetes to that of the general population if they just stay at normal weight.

We have also learned over the past few years that not all body fat is equally bad for your health.  People with central obesity, i.e. big bellies, have the highest risk for diabetes and other metabolic disorders, whereas people with the extra weight in their thighs and hips appear to be at no increased risk of disease.

The big challenge for most people is not only losing the excess weight, but keeping the weight off.   There is no magic to this process.  Any diet will work – as long as you eat fewer calories than you need. If you have diabetes and are taking insulin, you need to be careful to balance your meals and/or snacks with you insulin dose.   But, if you do have snacks, you will have to cut down what you eat at mealtime even more to lose weight.  Some people find it easiest to cut out certain foods, but I recommend keeping a balanced diet and simply cutting the portion you normally eat down by 30-50%.

Working with your physician, nurse or dietitian is important, but the bottom line is what you see when you step on the scale.  If you are overweight and the number on the scale is not decreasing, you are still eating too much.  So cut it out.  It could save your life.

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