Weight Loss Study Results Show that Calories Count

A study that ended several years ago was published this month in the American Journal of Clinical Nutrition, and so is making its way back into the news. The message cuts through much of the hype and confusion surrounding diets today.

How the Study Was Done

This study charted the weight gain or loss over a two year period for participants from the Boston, Massachusetts and Baton Rouge, Louisiana areas. Participants could be either gender, between the ages of 30 and 70, and were overweight at the start of the trial.   There were 1638 participants in this trial, divided equally between the two research sites. Eighty percent of the participants were able to complete the study, by providing a body weight measurement at the end of two years.

There were four different types of macronutrient profiles in the random diets that were assigned to participants. Two were high fat diets, one with a high carb-low protein ratio and one with low carb-high protein. The other two were low fat diet, each with the same high carb-low protein ratio and low carb-high protein ratios. Specifically, here are the percentages of macronutrients for each group:

  1. 20% fat, 15% protein, and 65% carbohydrates  (low fat, average protein)
  2. 20% fat, 25% protein, and 55% carbohydrates (low fat, high protein)
  3. 40% fat, 15% protein, and 45% carbohydrates (high fat, average protein)
  4. 40% fat, 25% protein, and 35% carbohydrates (high fat, high protein)

You can read the details of the methods used in this study in a New England Journal of Medicine article.

Weight Loss Study Results

At the end of the study the amount of weight loss and the change in waist measurement was the same between participants on a high and low protein diet, and participants on a high and low fat diet.  So those dietary changes did not have a significant impact on the amount of weight that was lost.  Here are a few of the interesting findings of this study:

  • Most of the weight loss occurred in the first six months, after which some participants began to slowly regain weight while some continued to lose. There was no significant difference among the diet groups for who gained or lost weight.
  • Over 50% of the participants ended up with a lower body weight at the end of the two year study.
  • All of the diets resulted in reduced risk factors for cardiovascular disease and diabetes, although some showed a stronger protection in certain areas. You can read the details at the NEJM link above.
  • Craving, fullness, and hunger and diet-satisfaction scores were similar at 6 months and at 2 years regardless of which diet a participant was following.
  • Attendance at the group sessions was a strong predictor of weight loss at the end of the two year period.  (Other studies have also showed that continued contact with the dieter results in a greater weight loss, suggesting that weight loss is influenced by behavioural factors.
  • At the end of the study participants across all four diets were reporting similar energy intakes and similar levels of physical activity.
  • Participants tended to adjust their levels of fat, protein and carbohydrate during the course of two years so that by the end their diets were much more similar than at the beginning. Weight loss results were similar across all four diets, showing that the percentage of macronutrients that you eat is not as important as adhering to a certain level of calories each day.

What Does This Mean for You?

The key here is that in order to lose weight you have to stick to your diet, regardless of whether that diet is low fat, low protein or low carb. There is no magical percentage of macronutrients that will help you to melt off the pounds. How can you stick to your diet for the long term? This study showed that social support and instruction in the group setting had a positive effect on weight loss.  Those people who were successful in losing weight also tended to self tailor the diet to one that they could eat long term, even though this meant that they changed the amount of fat, protein and carbohydrate they were eating. So if you can’t live without carbohydrates, there is no need to put yourself on a low carb diet. You probably won’t keep it up long term anyway. Instead enjoy your carbs but limit them to stay under a calorie level where you can lose weight or maintain your weight.