With the bar so low on science reporting this article was a welcome sight (How a Low-Carb Diet Might Help You Maintain a Healthy Weight) particularly from the New York Times. Researcher David Ludwig and team did a pretty nice study this time aimed at using a low carb diet for weight maintenance. Of course being Dr Ludwig he was aiming to show a metabolic advantage to the Low Carb diet compared with other higher carb diets. And his results showed that advantage.
The study itself is (Ebbeling Cara B, Feldman Henry A, Klein Gloria L, Wong Julia M W, Bielak Lisa, Steltz Sarah K et al. Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial BMJ 2018; 363 :k4583) (full pdf).
The study participants were:
164 adults aged 18-65 years with a body mass index of 25 or more
The goal of the study was to determine if the total body energy expenditure (commonly referred to as “metabolism”) was increased on the Lower Carb intervention:
The primary outcome was total energy expenditure, measured with doubly labeled water, by intention-to-treat analysis. Per protocol analysis included participants who maintained target weight loss, potentially providing a more precise effect estimate.
Secondary outcomes were resting energy expenditure, measures of physical activity, and levels of the metabolic hormones leptin and ghrelin.
In other words, does Low Carb help with weight maintenance?
Most of us have lost quite a bit of weight in our lifetimes and found that our bodies want to return to that previous weight – plus some weight in most cases. Everyone recognizes that it’s a lot harder to maintain a weight loss than to lose weight.
I really like that the study wasn’t about weight loss with the usual advantages in the low carb diets due to higher glycogen losses. When people refer to water weight they rarely understand the good part of that water weight is two-fold. One is less inflammation – which is a good thing. The other is that the water comes out due to glycogen stores dropping. There’s 3-4 grams of water bound up with every gram of glycogen. Losing the glycogen is important for getting to visceral fat, particularly in the liver and pancreas.
Back to the study… The study controlled the one variable which everyone claims is the sole reason low carb diets do better – protein. The claim is that when protein is held equal low carb diets don’t beat other diets. But this study held protein the same between the interventions:
During the test phase, high, moderate, and low carbohydrate diets varied in carbohydrate (60%, 40%, and 20% of total energy, respectively) and fat (20%, 40%, and 60%, respectively), with protein fixed at 20%
Even the lowest level of 20% is a reasonably low carbohydrate diet. It wasn’t the typical 5% of the ketogenic diet. Not only did the study control for protein, it also controlled for added sugar, saturated fat and sodium. Nice touch.
The relative amounts of added sugar (15% of total carbohydrate), saturated fat (35% of total fat), and sodium (3000 mg/2000 kcal) were held constant across diets.
Caloric intakes were adjusted to compensate for people continuing to drop weight.
The study had sufficient statistical power to tease out small differences between the groups that previous studies could not resolve (presumably the pilot Kevin Hall study which could not resolve differences due to lack of power (some of the conflict is documented by Dr Ludwig here).
The target of 135 completers provided 80% power, with 5% type I error, to detect a difference of 237 kcal/d in total energy expenditure change between one diet group and the other two diet groups.
The results showed an increase in energy expenditure as a function of carbohydrate restriction.
The difference in total energy expenditure was 209 to 278 kcal/d or about 50 to 70 kcal/d increase for every 10% decrease in the contribution of carbohydrate to total energy intake (1 kcal=4.18 kJ=0.00418 MJ).
Update 2018-11-19: Kevin Hall has critiqued the methodology of this study: Kevin D Hall, Juen Guo, Kong Y Chen, Rudolph L Leibel, Marc L Reitman, Michael Rosenbaum, Steven R. Smith, Eric Ravussin. Methodologic Issues in Doubly Labeled Water Measurements of Energy Expenditure During Very Low-Carbohydrate Diets. bioRxiv 403931.
DLW calculations failing to account for diet-specific energy imbalance effects on RQ erroneously suggest that very low carbohydrate diets substantially increase energy expenditure.
Update 2018-12-01: Kevin Hall is going down swinging on this subject. Here’s some of the continuing controversy (Author Response to Hall and Guo Regarding Data Reanalysis and Other Criticisms).