Low Carb diets often result in greater weight loss than low fat diets – this BLOG has linked to many of these studies.
One explanation hypothesized for the greater weight loss on Low Carb diets is the Low Carb diet is said to have an inherent metabolic advantage. This metabolic advantage should manifest itself in a greater resting energy expenditure. The paper looked at two possible mechanisms – triglyceride cycling and glyceroneogenesis.
The critics of the Low Carb diet say that the advantage is that the comparisons aren’t done by holding protein constant. Overfeeding protein is not the same as overfeeding carbs or fat since protein stimulates 24 hour energy expenditure and fat doesn’t (Overfeeding Protein – Carnivore Diet).
Look to the Science
A short term (6 weeks) small (4 subjects) study was done on obese women to compare the Low Carb and Low Fat diets which held energy (total calories) and protein constant ( Segal-Isaacson CJ, Johnson S, Tomuta V, Cowell B, Stein DT. A randomized trial comparing low-fat and low-carbohydrate diets matched for energy and protein. Obes Res. 2004 Nov;12 Suppl 2:130S-40S). The study concluded that there is no significant differences when controlling for protein.
Our results showed no significant weight loss, lipid, serum insulin, or glucose differences between the two diets.
The study was a decently formulated study but there were weaknesses:
- Small study – only 4 subjects
- No control group
- Older obese females only
- Very short duration (6 weeks)
- Low fat didn’t get super-low (20% of calories from fat)
- The Low Carb diet results in more weight loss but the study was too small to have statistical power
The good parts of the study were:
- Controlled feeding
- Matched total calories and protein – varying carbs and protein
- Decent protein level (30% of calories)
- Low carb was 5% of calories – good level
- Randomized control trial
- Cross-over design so the subjects ate both foods in random order
- Starches and fruit were the carbohydrate choices (not jelly beans)
- Deficit was relatively small (200 calories below REE which is a fairly large amount below TDEE depending on activity level)
At the end of the study they gave the participants the choice to continue on for a year. They were given the choice of the two diets and three of the four participants chose the Low Carb diet. However, the Low Carb participants raised their carbohydrate amount from 5% to 23% over the rest of the study so their weight loss partially reversed. There were several distinct advantages for the Low Carb diet.
Lipids were dramatically reduced on both diets, with a trend for greater triglyceride reduction on the VLC diet. Glucose levels were also reduced on both diets, with a trend for insulin reduction on the VLC diet
This fits my own experiences with protein and Low Carb. I’ve seen people stall for a long time and then break the stall by increasing their protein (and dropping their fat). My conclusion is that the ketogenic diet advantage does come from the higher protein intake of the diet. The diet often causes people to increase their consumption of meat which a high quality food.
Just Eat More Protein?
Protein alone doesn’t produce the same advantage that protein and Low Carb have together. This is shown in studies which substitute carbohydrates for protein (Blatt AD, Roe LS, Rolls BJ. Increasing the protein content of meals and its effect on daily energy intake. Journal of the American Dietetic Association. 2011;111(2):290-294).
This study showed that varying the protein content of several entrées consumed ad libitum did not differentially influence energy intake or affect ratings of satiety over a day. When the appearance, taste, fat content, and energy density were controlled, simply adding meat to lunch and dinner entrées to increase the protein content within commonly consumed amounts was not an effective strategy to reduce daily energy intake.
Sigma Nutrition Radio
Here’s a good program on this subject (SNR #64: Are Low-Carb Diets More Effective For Fat Loss?). tl/dl – Low Carb probably has better adherence than Low Fat diets.