A new study at the Children's Hospital of Philadelphia found that meal replacements like shakes, bars and prepackaged entrees aren't a good long-term solution for obese teens. For the new study, researchers randomly assigned 113 obese teens and their families to different diets for a year. One group of teens ate self-selected low-calorie meals not exceeding 1,300 to 1,500 total calories per day. The other group ate meal replacements (three SlimFast shakes and one prepackaged entree), along with five servings of fruits and vegetables. Four months into the study, participants in second group were randomized to a second-phase diet: some were put on the low-calorie self-selected diet, while the rest stayed on meal replacements.
At the four-month mark, all participants had lost weight, but the teens on meal replacements lost more — a 6.3% reduction in body mass index (BMI) versus 3.8% for the low-calorie group. But by the end of the one-year study, many participants had regained much of the weight they had lost, resulting in no significant differences in weight loss between the groups: on average, the teens had reduced their BMI 3.4% since the beginning of the study.
The results underscore one of the many difficulties of dieting: keeping the weight off long term. Many dieters regain weight because they can't stick to rigid eating programs for long: one-third of the participants in the current study dropped out before its conclusion. The monotony of the meal-replacement diet couldn't have helped either: teens in the meal-replacement group started out drinking SlimFasts 5.6 days a week (in Month 2); by the end of the study, they were only able to tolerate the shakes 1.6 days each week.
“The potential benefit of (meal replacement) in maintaining weight loss was not supported,” the researchers concluded. So for those of you who are gearing up to begin a weight-loss program in the New Year, it helps to remember that austerity isn't the best strategy long-term. Focus on variety — both with your diet and your exercise regimen — and manageability instead. A regular visit with Nastaran can ensure that you stay on track and keep the weight off long term.
Over the past several decades, the food industry has reduced the amount of saturated fat in many products, and the public has reduced the amount of saturated fat in their diet. However, there has been a wide variation in the types of nutrients that have replaced this saturated fat. For example, in many products saturated fats were replaced with trans fats, which have since been determined to be detrimental; and in the overall American diet saturated fat was generally replaced with increased consumption of refined carbohydrates and grains.
“The specific replacement nutrient for saturated fat may be very important,” said lead author Dariush Mozaffarian, assistant professor in the department of epidemiology at HSPH and the department of medicine at Harvard Medical School. “Our findings suggest that polyunsaturated fats would be a preferred replacement for saturated fats for better heart health.”
Results from prior individual randomized controlled trials of saturated fat reduction and heart disease events were very mixed, with most showing no significant effects. Other trials focused only on blood cholesterol levels, which are an indirect marker of risk. Large observational studies have also generally shown no relationship between saturated fat consumption and risk of heart disease events; for example, earlier this month in the American Journal of Clinical Nutrition, researchers from HSPH and Children's Hospital Oakland Research Institute performed a pooled meta-analysis of prior observational studies and found no evidence that overall consumption of saturated fat was related to risk of coronary heart disease or stroke events.
Some of these mixed findings may relate to absence of prior focus on the specific replacement nutrient for saturated fat; in other words, was saturated fat replaced primarily with carbohydrate, monounsaturated fats such as in olive oil, or polyunsaturated fats such as in most vegetable oils?
Mozaffarian and his HSPH colleagues, Renata Micha and Sarah Wallace, performed a systematic review and meta-analysis of all randomized controlled trials through June 2009 in which participants specifically increased their polyunsaturated fat consumption as a replacement for saturated fat and in which coronary heart disease events were documented. Eight trials met the inclusion criteria, totaling 13,614 participants with 1,042 coronary heart disease events.
The meta-analysis of the trials showed that increasing polyunsaturated fat consumption as a replacement for saturated fat reduced the risk of coronary heart disease events by 19%. For every 5% increase (measured as total energy) in polyunsaturated fat consumption, coronary heart disease risk was reduced by 10%. This is now just the second dietary intervention–consuming long-chain omega-3 fatty acids is the first — to show a reduction in coronary heart disease events in randomized controlled trials.
Currently, the Institute of Medicine guidelines recommend that a range of 5%-10% energy consumption come from polyunsaturated fats. In addition, some scientists and organizations have recently suggested that consumption of polyunsaturated fats (largely “omega-6” fatty acids) should actually be reduced due to theoretical concerns that such consumption could increase coronary heart disease risk.
The results from this study suggest that polyunsaturated fats from vegetable oils may be an optimal replacement for saturated fats, an important finding for dietary guidelines and for when food manufacturers and restaurants are making decisions on how to reduce saturated fat in their products. The findings also suggest that an upper limit of 10% energy consumption from polyunsaturated fats may be too low, as the participants in these trials who reduced their risk were consuming about 15% energy from polyunsaturated fats.
Support for this study was provided by the National Heart, Lung, and Blood Institute, NIH and a Searle Scholar Award from the Searle Funds at the Chicago Community Trust.