Doctor's hand with very fat male patient 2048 × 1360

We have known for a number of years that changes in lifestyle, such as diet, weight loss, and increased physical activity, can slow and may prevent the onset of Type 2 diabetes in individuals who have impaired glucose tolerance.  But we didn’t know which of those lifestyle changes were the most important.

A new study published in the September issue of Diabetes Care sheds some light on this question. Richard F. Hamman, MD, PH.D and his colleagues analyzed data from the Diabetes Prevention Program to try to learn more about the relative contributions of weight loss, diet, and physical activity on diabetes prevention.


The Diabetes Prevention Program

The Diabetes Prevention Program is a landmark study that documented a 58% reduction in the incidence of diabetes over three years in people who participated in an “Intensive Lifestyle?” program, compared to others who did not have access to that program. The intensive lifestyle (ILS) program participants set weight loss, diet, and exercise goals as follows:

  • Reduce weight by 7% from their baseline weight at the start of the study
  • Maintain at least 150 minutes per week of moderate physical activity
  • Reduce dietary fat to less than 25% of total calories
  • If weight loss was not achieved by lowering fat, calorie goals were introduced

ILS participants met with a lifestyle counselor weekly for 16 weeks and at least twice a month after that. Group classes and campaigns were used to help keep people on track.

Because there was variation amongst the ILS participants in how well they complied with the program and whether or not they achieved their goals, the researchers in the current study were able to analyze data from this group to try to ascertain which of the three lifestyle changes (weight loss, dietary fat reduction, or physical activity) was more important when it came to preventing diabetes.

They divided the ILS participants into eight groups based on whether or not they lost weight and/or met their weight, exercise, and dietary fat goals. Here is how the groups broke down:

Group 1 2 3 4 5 6 7 8
At weight goal No No No No Yes Yes Yes Yes
At exercise goal No No Yes Yes No No Yes Yes
At fat goal No Yes No Yes No Yes No Yes
Average weight loss in kilograms -1.5 -2.5 -2.2 -3.5 -11.5 -11.5 -11.8 -13.4
Number of people in the group 134 32 228 103 51 34 208 187

There was no reduction in diabetes risk in Group 1, the group which did not lose weight nor meet the ILS goals. But as people met more and more goals and lost weight more and more weight, their diabetes risk decreased. The lowest risk was in Group 8, the group that met all of the goals and lost the most amount of weight.

Further analysis revealed that weight loss was the dominant determinant of the reduced risk of diabetes. Increased physical activity and reduction in dietary fat predicted weight loss. The researchers estimated that a 5 kilogram (11 pounds) weight loss over time could account for a 55% reduction in the risk of diabetes over the 3+ years of this study. In fact, they conclude that there was a 16% reduction in diabetes risk, after adjustment for changes in dietary fat and physical activity, for every kilogram (2.2 pounds) of weight loss.

This is not to say that physical activity was unimportant. There was a 44% reduction in diabetes incidence for participants who met the physical activity goal of 150 minutes of moderate intensity activity per week even if they did not lose much weight (compare Groups 3 and 4 to Groups 1 and 2 in the table above). This makes sense since other studies have shown that physical activity has a positive effect on insulin sensitivity even in individuals who do not lose weight.


The bottom line

So the bottom line is people at risk for Type 2 diabetes need to do whatever it takes to lose weight. That means moderate to vigorous physical activity most days of the week. It also means eating a reduced calorie diet to achieve and maintain significant weight loss. Reducing fat in the diet is one way to reduce calories, but it is not the only way. You also need to be sure you eat fewer calories than you burn.

Sounds hard, right? Is it worth it? You can bet your life on it.