In another study, this one conducted in Illinois, 24 women aged 45–56 years were assigned to either a higher-protein or a lower-protein diet for 10 weeks. While the two groups lost about the same amount of weight, the women who ate more protein experienced significantly greater loss of body fat.
While weight loss may be the most important goal for people following a diet, the actual changes in body composition — or proportions of fat to muscle — are more important for your health. Excessive body-fat stores, especially fat stored in the abdomen, are strongly linked to obesity, diabetes, cancer, and cardiovascular disease.
Glucose and insulin levels
Finding the right meal plan is not just important for achieving and maintaining a healthy weight; it’s important for blood glucose control as well. Some studies have investigated whether a higher-protein diet may help in this respect.
One such study involved 10 obese people with diabetes. The study participants initially followed their normal diet for 7 days, then followed a very-low-carbohydrate diet (with about 20 grams of carbohydrate a day) for 14 days. Although the researchers didn’t restrict overall calorie intake, the effect of restricting carbohydrate intake spontaneously lowered participants’ calorie intake by about 1,000 calories per day. As a result of the 14-day dietary change, participants lost weight, lowered blood glucose levels, improved insulin sensitivity, and lowered triglyceride and cholesterol levels. However, it is unknown whether this diet could be continued over a longer term, whether its positive effects would continue, and what the effect of a greatly reduced fiber intake would be.
Adding exercise to diet
Regular exercise can improve diabetes control and heart disease risk and help with weight maintenance in many of the same ways that diet can. It can additionally build muscle (which burns more calories than fat) and increase strength and stamina.
To see what the effects would be of following a higher-protein diet while also following an exercise program, researchers in Illinois devised a study to find out. The study participants were 48 obese women and, as in the other studies described here, all consumed the same number of calories, but some consumed more protein and less carbohydrate, while others consumed less protein and more carbohydrate. In addition, some were educated about physical activity and encouraged to exercise voluntarily (this was the exercise control group), while others had a supervised exercise program that included aerobic activities and resistance training.
After 16 weeks, the researchers found that the women who ate more protein lost more total body weight and body fat than those who consumed more carbohydrate. However, the women in the supervised exercise group lost more body fat than those in the exercise control group, no matter which diet was followed.
The effects of a higher-protein diet and exercise were additive: The women in the higher-protein plus supervised exercise group experienced a 21.4% reduction of total body fat. In comparison, the women who followed the higher-carbohydrate diet and were in the exercise control group saw a 12.8% reduction in total body fat. In addition, the women in the higher-protein plus supervised exercise group were better able to maintain their levels of muscle tissue, while those in the higher-carbohydrate and exercise control groups lost almost 5% of their initial muscle mass.
Composing your own meal plan
Much debate continues over the ideal proportion of nutrients for people with diabetes, people trying to lose weight, and people facing both challenges. Luckily, scientific research is ongoing as well, so someday there may be real answers and not just the claims of popular diet books. It’s possible — even likely — that diet composition is not a one-size-fits-all proposition.