POSTED 13 MARCH 2008
Diet: Weighty answer to diabetes and metabolic syndrome, or false hope?
Since being overweight or obese are major contributors to metabolic syndrome and type 2 diabetes, diet and exercise were the traditional focus in diabetes prevention, but losing weight is easier said than done, as Richard Bergman of the University of Southern California notes. "We've heard many times about a lifestyle approach to weight loss, but that only lasts a short period, 97 percent of the people that lose weight by diet and exercise gain it back within three to five years; it's very difficult to cause long-term improvement."
Some research studies have found that weight loss can be sustained with enough effort, he adds. "In Finland, they took people for five years, used lots of counseling sessions, and this reduced the risk of diabetes very significantly, but ... this is generally very ineffective in a real-life situation. People who are initially lean think it's very easy, but it is almost impossible for people to lose weight this way." An obese person who has lost weight "is not the same. Their energy utilization rates are very low, and they gain the weight back even on a low-calorie diet.
Doctor: Lose it or lose it!
Nonetheless, research on metabolic syndrome continues to show how much difference lifestyle can make -- for better or worse -- in the progression to diabetes. Take, for example, the landmark Diabetes Prevention Program, which studied 3,234 overweight people who had impaired glucose tolerance -- two key elements of metabolic syndrome. A combination of diet and exercise reduced their risk of diabetes by 41 percent, far better than the diabetes drug metformin, which cut the risk by 17 percent (see #1 in the bibliography).
The Diabetes Prevention Program was so effective that it ended one year early, to allow the control group to get the diet-and-exercise counseling, and the results were convincing to cardiologist Lopez-Jimenez. "They only lost about four pounds, but for patients who became physically active and were trying to eat better, the chance of developing diabetes went way down. It's hard to find somebody with metabolic syndrome who is very active, exercises, has a good diet. Everybody who has metabolic syndrome needs behavioral change."
The benefits of exercise, combined with minor weight loss, have caused some doctors to shift the focus away from the bathroom scale. At Mayo, Lopez-Jimenez, says, "We try to stay away from calling this just a weight-loss goal. And we don't say, 'Get some exercise, get a good diet, I'll see you later.'" Mayo doctors prescribe the quality and quantity of exercise, and work with the patients to overcome any physical limitations -- and to cope with the nasty Minnesota winter.
Eat less. Exercise more.
What do recent studies show about mother's advice -- eat a good diet and get some exercise -- tell us about metabolic syndrome and diabetes?
Weight training may help: In a new study of Asian Indians, progressive resistance training benefited three key parts of metabolic syndrome: insulin resistance, blood triglycerides (harmful fats), and fasting glucose (see #2 in the bibliography).
Exercise helps without weight loss: A study of 115 adults at the Johns Hopkins Medical Institution found that exercise improved blood pressure, total cholesterol, and insulin sensitivity. But the cause was neither the increase in fitness nor weight loss, but reductions in total body fat and abdominal fat (see #3 in the bibliography or stick around for more on the role of abdominal fat in metabolic syndrome.)
Being active now can pay off in old age: In 2000, Norwegian researchers looked at men who had enrolled in the Oslo Study of health in 1972, and found a 40 percent reduction in the development of metabolic syndrome among men who had been physically active during leisure time (see #4 in the bibliography).
Targeted programs can help: A study in Montreal, Canada, looked at people who either already had type 2, or seemed headed for it. The 29 people who completed DiabetAction, which helped select the optimum exercise for reducing diabetic tendencies, showed significant reductions in body weight, waist circumference, resting heart rate, blood pressure, and the prevalence of metabolic syndrome six months later (see #5 in the bibliography).
Even "moderate" interventions can work better than simple advice from the family doctor: Among 335 Italian adults who were on the road to diabetes, professional advice led to more exercise and improvement in most markers for metabolic syndrome. This group had a 31 percent reduction in the risk of diabetes, but "usual care by family physicians was ineffective at modifying progressive metabolic deterioration" (see #6 in the bibliography).
Too much sitting may be unhealthy: A recent look at the role of sedentary behaviors in death, cardiovascular disease, type 2 diabetes and metabolic syndrome concluded that the growing trend toward inactivity suggests that "the average non-exercising person may become even more metabolically unfit in the coming years if they sit too much" (see #7 in the bibliography).
Combination of ingredients?
So what's up? Nobody questions the metabolic benefits of losing weight. But Edward Weiss, assistant professor of nutrition and dietetics at Saint Louis University, says exercise confers a separate set of benefits. "A number of studies with a wide array of designs are in pretty good agreement: If you start an exercise program and don't lose weight, you still can be expected to have substantial [diabetes] risk reduction."
Photo: Eric Zuelow
But if exercise alone is helpful, and losing weight alone is helpful, shouldn't losing weight through exercise produce even more benefits? That's what Weiss expected when he compared weight loss from calorie reduction to weight loss due to exercise. Each group, however, had similar improvements in body weight, glucose tolerance and insulin sensitivity. That result, Weiss says, was "mind-boggling. ... Our hypothesis was that if exercise and weight loss each are independently helpful, you should get a greater benefit from the combination, but we did not see that" (see #8 in the bibliography).
The benefits of exercise may center on insulin, Weiss says. "It's most likely that skeletal muscle adapts to exercise, so any given amount of insulin will take more glucose out of the bloodstream, and into intercellular space. Insulin's action on glucose clearance is improved; the muscle is more sensitive."
Caloric restriction seems to work through a partly different mechanism that may involve reductions in oxidative stress and inflammation or even intestinal adaptations Because interventions that act through different mechanisms typically provide greater benefits when combined than either would alone, Weiss suspects that a combination of caloric restriction and exercise may be even more effective in the struggle against metabolic syndrome.
In the meantime, if your exercising MO includes snarfing HammerBars and guzzling SugarAde, you may want to consider hoofing or pedaling on an empty stomach, to get more benefit from two separate weapons against metabolic syndrome.
Could metabolic syndrome help us understand the relationship of diabetes and cardiovascular disease?
Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive