Popular Diets Rarely Offer Long-Term Success

Nearly two out of three Americans are now considered overweight or obese, the government says - and most of us know who we are and don't like the way we look or feel. That's why so many of us make New Year's resolutions to lose weight, become more active, and feel better.

Among popular diets - Atkins and South Beach, Weight Watchers, Mediterranean, DASH, Sugar Busters, and many more - are any especially effective? Hard to say, says the Annals of Internal Medicine in a 2005 article that concluded that there's not enough evidence for a definitive judgment. It said: "With the exception of one trial of Weight Watchers, the evidence to support the use of the major commercial and self-help weight loss programs is suboptimal. Controlled trials are needed to assess the efficacy and cost-effectiveness of these interventions."

The Medical College of Wisconsin is currently studying the effects of weight-loss diets and exercise, but the research is focused on how they affect vascular health, says Shane Phillips, PhD, an Instructor in Cardiovascular Medicine. Although the study initially compared the merits of a low-carbohydrate diet with those of a low-fat diet on heart health, the important factor for weight loss is still calories, Dr. Phillips says.

Calories Still Count
"The basic principle and premise of any diet comes down to 'calories in versus calories out,'" he says, referring to how many calories you consume, how well your body metabolizes or burns up those calories, and how active you are. Your metabolic rate can be influenced by genetics, he adds.

He is working with David Gutterman, MD, Senior Associate Dean for Research at the Medical College, as well as the Northwestern Mutual Professor of Cardiology in the Division of Cardiovascular Medicine and the Cardiovascular Research Center.

Because diets like Atkins emphasize high protein and fat but sharply limit carbohydrates, some fear such regimens may be bad for the heart. Not so, according to a 2003 study published in the New England Journal of Medicine. It found that the low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease versus a low-fat diet, and it noted that the low-carbohydrate diet produced a greater weight loss by about 4% than did the low-fat diet - but only for the first six months.

The article did add this sobering conclusion, however: "But the differences were not significant after one year. Adherence was poor, and attrition was high in both groups. Longer and larger studies are required to determine the long-term safety and efficacy of low-carbohydrate, high-protein, high-fat diets."

A later study that tested the effects of a low-carbohydrate diet on 83,000 women nurses, published in the New England Journal in November 2006, found no evidence of an association between low-carbohydrate diets and increased cardiovascular risk, even when those diets were high in saturated fats.

Beware of High Glycemic Load
But, importantly, that study did show that diets with a "high glycemic load" were 1.9 times more likely to promote heart disease. "That refers to the amount and type of sugar in the diet," Dr. Phillips says.

"Both fats and carbohydrates are essential for health and should not be eliminated from the diet," he cautions. "But it depends on the type of fat and the type of carbohydrate," he said.

Excessive trans fats and sugars can add weight and carry health risks. Trans fats can raise cholesterol levels and increase the risk of heart disease. Even worse, trans fats can also raise triglycerides and lower the level of the so-called good cholesterol, or the high-density lipoproteins (HDLs), while increasing the levels of the bad cholesterol, or LDLs, the low-density lipoproteins.

"Vegetables and fruits have carbohydrates, and tend to have lower glycemic loads than sweets," he adds. "The carbs in fruits, vegetables, and whole grain breads are complex carbohydrates. They take longer to metabolize, and they tend to raise blood sugar less rapidly after a meal and therefore are lower on the glycemic index. The simple sugars - like the kind found in cakes and candies - are digested quickly and tend to have a higher glycemic load."

Keeping the glycemic load under control is important, because the amount of carbohydrate consumed also affects blood sugar levels and insulin responses.

After a high-glycemic-load meal, blood glucose levels rise more rapidly and insulin demand is greater than after a low-glycemic-load meal. In the nurses' study, those participants with the highest dietary glycemic loads not only gained more weight, they were also 37% more likely to develop type 2 diabetes over six years than women with the lowest dietary glycemic loads.

High dietary glycemic loads are also associated with increased triglyceride levels and decreased HDL cholesterol, both cardiovascular disease risk factors.

To lower glycemic load, nutritionists recommend such strategies as:

• Increasing the amount of whole grains, nuts, legumes, fruits and non-starchy vegetables
• Reducing the amount of starchy high-glycemic index foods like potatoes, white rice and white bread
• Decreasing the consumption of sugary foods like cookies, cakes, candy and soft drinks

Diet Drop-Outs
Dr. Phillips has observed that many popular diets "seem to work in the beginning because they are designed around a rapid weight loss, which is encouraging" for the dieter. "But typically, it is difficult to maintain the same rate of weight loss for long."

Indeed, in 2005, a survey by the market research firm InsightExpress reported that more than 50% of Americans who had tried a low-carbohydrate diet had given up within a few months.

One reason low-carbohydrate diets are successful for some people is "they induce a feeling of satiety," he says. "When people add more whole grains, nuts, legumes, fruits and some vegetables into their diet along with protein, they tend to feel satisfied, and they actually eat less."

Another way to help control weight, says Dr. Phillips - who has a master's degree in physical therapy - is to add more activity, which burns calories. "It doesn't have to be a vigorous workout," he says. "Move around more. Walk 20 or 30 minutes a day. Use the stairs instead of the elevator."

Finally, he recommends anyone contemplating a weight-reducing diet consult his or her physician and possibly a dietitian for counseling to determine the best individualized dietary strategy.

Barbara Abel
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.