Since the Joslin guideline was written for people who are overweight or obese and weight loss is one of the primary goals, calorie reduction is also part of the plan. Daily calories should be reduced by 250 to 500, and total daily calorie intake should be no less than 1,000–1,200 for women and no less than 1,200–1,600 for men.
What the research shows
As mentioned earlier, researchers have in recent years been testing various diets with differing proportions of carbohydrate, fat, and protein to see whether and how they affect the body differently. In many if not most cases, the number of calories that study participants consume is restricted, and when that is true, participants tend to lose weight no matter what the composition of their diet. Indeed, higher-protein, lower-carbohydrate diets do not consistently cause more weight loss than lower-protein, higher-carbohydrate diets.
However, higher-protein, lower-carbohydrate diets may nonetheless offer certain benefits, such as lower triglycerides (the most abundant type of blood fat), a higher high-density lipoprotein (HDL, or “good”) cholesterol level, loss of more body fat, maintenance of more lean body tissue, and less hunger while restricting calories.
Less hunger. Researchers at Arizona State University had 20 healthy adults follow one of two diets. Both diets restricted the number of calories per day, and both got less than 30% of calories from fat. However, one got 15% of calories from protein, and the other got 30% of calories from protein. After six weeks, both groups reported an average weight loss of 6% of body weight and a similar decrease in fat mass. However, in the first month of the study, the people with the higher protein intake reported more satisfaction and less hunger.
Lower body fat and triglycerides. A 12-week study completed in Australia had 100 overweight women follow calorie-restricted, low-fat diets. One group had a higher protein intake, and one a higher carbohydrate intake. Both groups lost similar amounts of weight. But among the women with high triglycerides, those who ate a higher-protein diet lost significantly more body fat than those who ate a higher-carbohydrate diet. The women who ate more protein also experienced a significantly greater decrease in triglycerides.
More initial weight loss. A one-year study compared the weight loss achieved through following a low-carbohydrate, high-protein, high-fat diet (based on the Atkins diet) with that achieved through following a low-calorie, high-carbohydrate, low-fat diet (containing about 60% carbohydrate, 15% protein, and 30% fat). The group that followed the Atkins diet was instructed to limit carbohydrate to 20 grams per day for the first two weeks, then increase that amount gradually. They were not instructed to limit protein or fat.
The study participants were 63 obese men and women. After 3 months, the Atkins diet group had a greater weight loss (6.8% of body weight lost), and after 6 months, the Atkins diet group again had a greater weight loss (7.0% of body weight lost). After 12 months, however, the weight loss between groups was not different.
The authors concluded that a lower-carbohydrate diet produces greater weight loss in the early stages, but that difficulty following such a plan may result in total amount of weight loss after 12 months being no different from the weight loss achieved with a higher-carbohydrate diet.
Lower triglycerides, higher HDL. Two studies conducted by researchers at the University of Illinois reported that when consuming a diet with a higher proportion of protein, people experienced significantly greater decreases in triglycerides, as well as greater maintenance of high-density lipoprotein (HDL, or “good”) cholesterol.
Less body fat. A study conducted in Australia followed 54 obese men and women with Type 2 diabetes over an eight-week period. All participants consumed about 1,600 calories per day, but one group’s diet consisted of 55% carbohydrate, 16% protein, and 26% fat (the lower-protein diet), and the other’s had 42% carbohydrate, 28% protein, and 28% fat (the higher-protein diet). After eight weeks, the total amount of weight lost was similar between groups. However, men lost more weight on the lower-protein diet, while women lost more weight on the higher-protein diet. Additionally, women who followed the higher-protein diet lost almost two times more body fat than women who ate more carbohydrate, but no such differences in body fat were found in men.