Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial (Ebbeling et al., 2018)
This is another NuSi study designed to evaluate certain aspects of the carb/insulin model of obesity. Understanding the design of this study is critical to being able to properly evaluate the results.
1. All food was provided, all the diets were healthy, and most people complied.
2. This was a very expensive study. They used great methods.
Study design: during the "Run-in diet," everyone followed the same diet (C/F/P: 45%/30%/25%) at 40% caloric restriction in order to lose about 10% of their initial body weight.
Importantly, insulin sensitivity was assessed and this may have influenced what happened next, in the weight maintenance phase. I used to put a lot of weight on this theory -- eg, the top 25% most insulin sensitive people will do better on low fat whereas the bottom 25% insulin sensitive people (the most insulin resistant, ie) will do better on low carb -- this theory has fared better or worse depending on which study you look at. In this study, it did pretty well.
In the end, we had 38 people in the entering into the high carb arm of the weight maintenance phase and 43 on low carb.
Remember, they all lost weight on the same diet. Now they're being fed enough to maintain body weight (low carb, moderate carb, or high carb) and we're measuring stuff.
Weight maintenance diets (not to be redundant, but again, this is after they all lost weight on the same diet and calories were dynamically adjusted so they could stay at their new lower body weight):
Main outcome measure: total energy expenditure. This is basically how much more you can eat or how much less exercise you need to maintain the weight loss. And this is where the magic happened.
After weight loss (on the same 40% calorie restricted diets), everyone's total energy expenditure declined as expected. After 20 weeks of weight maintenance on low or high carb, however, total energy expenditure recovered significantly more on low carb... by 278 kcal/d more than on high carb. When adjusted for sex, ethnicity, race, and age; pre-weight loss values for BMI, percentage lean mass, and total energy expenditure; and weight loss from pre-weight loss to the start of the trial, this value was reduced to 249 kcal.
In the figure above, you can see there was little if any recovery of total energy expenditure in the low fat group.
Leptin was higher and ghrelin was lower in the low carb group suggesting that in an ad libitum context, this may have led to greater weight loss.
Now onto that other theory, the IR/IS-LC/LF theory, total energy expenditure in the most insulin resistant people barely recovered and actually slightly declined in the high carb group whereas there was a much greater improvement in the low carb group. What's giving this theory more traction from this study is the magnitude of the effect. The difference between low carb and high carb was 478 kcal/d. Almost twice that observed when people weren't subgrouped by insulin sensitivity! This didn't matter very much in the participants who were the most insulin sensitive.
and viewed in another #context:
That's all for now!
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