Energy and macronutrient intake after gastric bypass surgery

The Study
Gastric bypass surgery is an effective strategy for weight loss in the severely obese when diet and exercise has not been effective. However, in most cases, 40-50% of lost weight is regained after several years and it is not clear why this is the case.

In this study, 16 women were followed for 3 years after bypass surgery. Total energy, lean body mass, and basal metabolic rate were measured at regular intervals during the follow-up. By the end of 12 months, the women had lost an average of 87 lbs.

At baseline, calorie consumption was 2,072 per day.

At 1 month post surgery, it dropped down to 681 calories.

At 12 months post surgery, it increased to 1240.

At 36 months, it increased to 1,448 calories.

As far as basal metabolic rate:

At baseline, it was 1.1 kcal/minute.

At 3 months it was .93 kcal/minute.

At 12 months it was .86 kcal/minute.

At 36 months is was .85 kcal/minute.

By the end of 1 month, 51.6% of weight lost was lean body mass. By the end of one year, 24.5% of weight lost was lean body mass. By the end of 36 months, 30% of weight lost was lean body mass. American Journal of Clinical Nutrition 2016; 103:18-24.

Take Home Message

This is a really important study, not just for those who have bypass surgery, but for everyone looking to keep lost weight off for good. Over the 3 years of this study, we saw a gradual increase in caloric consumption, a gradual decrease in basal metabolic rate, and a very significant loss in lean body mass.

Remember, lean body mass burns calories and is highly related to metabolism. You lose muscle, your metabolism drops and weight regain is far more likely. 

This study shows why a lot of people who get gastric bypass surgery regain their weight. They are the same reasons why the rest of us regain our weight; calories shoot back up and metabolism drops. 

The body may lower metabolism in response to weight loss. There is not much we can do about that. However, we can minimize loss of muscle mass by lifting weights consistently throughout the weight loss process and during weight maintenance. Keeping a close eye on caloric consumption is also essential to keeping the weight off.

This study would have been perfect if half the women were randomized to a weight lifting routine post surgery to compare basal metabolic rates and percent lean body mass lost.