The present systematic review examined the effectiveness of weight management interventions comparing diets with varying macronutrient distributions on BMI and cardiometabolic risk factors in overweight or obese children and adolescents. A systematic search of seven databases for the period 1975−2013 identified 14 eligible randomized or quasi-randomized controlled trials conducted with 6–18-year-old subjects. Seven trials compared a low-fat (≤33% energy or <40 g/day) to an isocaloric (n = 2) or ad libitum (n = 5) low-carbohydrate diet (<20% energy or <60 g/day). Meta-analysis indicated a greater reduction in BMI in the low-carbohydrate group immediately after dietary intervention; however, the quality of the studies was limited and cardiometabolic benefits were inconsistent. Six trials compared increased-protein diets (19–30% energy) to isocaloric standard-protein diets (15–20% energy) and one compared an increased-fat diet (40% energy) to an isocaloric standard-fat diet (27% energy); there were no differences in outcomes in these studies. Current evidence suggests that improved weight status can be achieved in overweight or obese children and adolescents irrespective of the macronutrient distribution of a reduced-energy diet. Tailoring the macronutrient content to target specific cardiometabolic risk factors, such as a low-carbohydrate diet to treat insulin resistance, may be possible, but further research is needed before specific recommendations can be made.
Alex’s Notes: Children are fat. They shouldn’t be, but they are. I’ve previously talked about the importance of muscle mass in adolescent health, as well as the effectiveness of high-intensity training on promoting adolescent health parameters. However, exercise is only a part of the puzzle. Diet and nutrition is the other critically important factor that influences health and must be addressed in the growing population of childhood obesity. Up to this point, numerous studies have compared various diets on weight and cardiometabolic parameters of youth, but nothing conclusive has been found. The aim of this review and meta-analysis was to examine the effectiveness of diets of various macronutrient make-ups as part of a weight management program in overweight and obese children.
In adults, it has been suggested that low-carbohydrate diets are more effective than low-fat diets for both weight loss and cardiometabolic parameters after six months. Moreover, high-protein diets have been shown to produce greater reductions in weight and fat-mass, with greater preservation of muscle, increased energy expenditure, and increased satiety. Yet, children are not adults and diets must be tailored to the individual. In total, 14 studies were included in the review and divided into three categories, which I figure will be easiest to address individually below.
Low-carbohydrate vs. low-fat
A diet was considered low-carbohydrate if subjects consumed less than 60g or a maximum of 20% of total calorie intake of carbohydrates daily. Seven studies met inclusion that compared low-carbohydrate and ketogenic diets to low-fat diets that there less than 33% of total calories or less than 40 grams per day. All the studies also restricted calories and thus all reported improvements in weight, with four of the studies showing no difference between treatments, and the other three showing an advantage for the low-carbohydrate group. Three studies also reported improvements in total and LDL cholesterol and triglycerides from baseline, but no difference between groups. This is not all that surprising since weight-loss itself improves blood lipids. The meta-analysis concluded that there was a significant decrease in BMI for the low-carbohydrate group compared to the low-fat group, but this was only by about 1.5 points and that is probably due to differences in muscle glycogen and water content that is lost during carbohydrate restriction. Thus, low-carbohydrate diets may be more beneficial in the short-term and improve some additional aspects of health, but overall the results are inconsistent.
High vs. standard protein
Six studies investigated the manipulation of protein on weight loss. All six of the studies compared two isocaloric diets with equal fat content of 25-35% of total calories, and the differences being in protein and carbohydrate amount. In the standard protein diet, carbohydrate was moderate to high at 35-50% of total calories and protein ranged from 15-20%. The high protein diets increased the protein to 19-30% of total calories at the expense of carbohydrates. In every study, there were improvements in weight and cardiometabolic parameters but with no differences in either between diets at any time point and the meta-analysis confirmed this.
What this should make perfectly clear is that calories do matter, since the diets were of equal caloric content. However, at the same time, the isocaloric nature of the diets may have blunted the satiating effects of protein that are believed to contribute to its beneficial effects during ad libitum food intake. Then again, three of the studies did report feelings of fullness and hunger with no difference between groups. But even here I must take issue. The standard-protein diets used 15-20% of total calories, which during a time of calorie restriction was only amounting to perhaps 1g/kg of protein per day. In children that is exceptionally low simply because their weight is low. Thus, the “high” protein diets they compared to may actually be considered “normal” protein diets.
Increased fat vs. standard fat
This category only had one study in it that compared a 40% fat diet to a 27% fat diet, with the difference coming from carbohydrates and protein being held constant at 18%. There were no differences in weight or fat-loss between groups. The only significant difference was an increase in triglycerides in the standard-fat group compared to low-fat group after the end of a eucaloric phase.
Given the results of this review and meta-analysis, it appears that there is no “best” diet for children so long as they are eating a hypocaloric diet that promotes weight-loss. The most effective approach will be the one that allows for the greatest adherence to the diet, as well as one that promotes the greatest feelings of energy and wellbeing that will spur more physical activity. However, due to the methodological flaws of the studies in the protein categories, I am still inclined to believe that a truly high-protein diet in a free-living scenario will be most beneficial. How the carbohydrates and fats are split up will depend on the child’s specific preferences, needs, and cardiometabolic profile.