Re: Swedish health advisory body says too much carbohydrate, not fat, leads to obesity
Nina Rehnqvist, in her response, states
"Second, it is only in the short term that advice consisting of diets characterized as moderate and low carb are associated with a slightly larger reduction in weight than diets low in fat (6 months). No differences were seen after 12 and 24 months."
This statement is wrong without further qualification. After 12 and 24 months in a single trial the number of people who go back to eating as they did before becomes so great (around 50-40%) that the difference between diets in randomised groups, though still present, is often no longer statistically significant.
For example
"Persons on the low-carbohydrate diet who dropped out lost less weight than those who completed the study (change, -0.2 ± 7.6 kg vs. -7.3 ± 8.3 kg, respectively; mean difference, -7.1 kg [CI, -11.6 kg to -2.8 kg]; P = 0.003)."
"In contrast, weight loss was not significantly different for those on the conventional diet, whether they dropped out or completed the study (change, -2.2 ± 9.5 kg vs. -3.7 ± 7.7, respectively; mean difference, -1.5 kg [CI, -5.7 kg to 2.7 kg]; P > 0.2). Nevertheless, the difference in weight loss between the 2 diet groups for those who dropped out of the study was not significant (P >0.2)."[1]
The numbers of drop-outs is similar in both groups, and the 12 month difference with these drop-outs included is not significant.
However, this is not a test of what any diet does. If people relapse when they stop taking the drug that controls a condition, we never take this as evidence that the drug is only effective in the short term.
A further consideration is, that outside of the diet trial, the mean weight of this population would likely have increased.
Yet another consideration is that the LCHF diets in most studies are ad lib (no conscious attempt made to count calories or to undereat), whereas the low-fat diets require restricting calories, presumably because they would not be effective otherwise.
This difference can be extrapolated to the real world, where diets are usually eaten ad lib, to explain the rise in obesity following the introduction of novel advice to restrict dietary fat and government campaigns to increase production of low-fat food products.[2]
Rapid Response:
Re: Swedish health advisory body says too much carbohydrate, not fat, leads to obesity
Nina Rehnqvist, in her response, states
"Second, it is only in the short term that advice consisting of diets characterized as moderate and low carb are associated with a slightly larger reduction in weight than diets low in fat (6 months). No differences were seen after 12 and 24 months."
This statement is wrong without further qualification. After 12 and 24 months in a single trial the number of people who go back to eating as they did before becomes so great (around 50-40%) that the difference between diets in randomised groups, though still present, is often no longer statistically significant.
For example
"Persons on the low-carbohydrate diet who dropped out lost less weight than those who completed the study (change, -0.2 ± 7.6 kg vs. -7.3 ± 8.3 kg, respectively; mean difference, -7.1 kg [CI, -11.6 kg to -2.8 kg]; P = 0.003)."
"In contrast, weight loss was not significantly different for those on the conventional diet, whether they dropped out or completed the study (change, -2.2 ± 9.5 kg vs. -3.7 ± 7.7, respectively; mean difference, -1.5 kg [CI, -5.7 kg to 2.7 kg]; P > 0.2). Nevertheless, the difference in weight loss between the 2 diet groups for those who dropped out of the study was not significant (P >0.2)."[1]
The numbers of drop-outs is similar in both groups, and the 12 month difference with these drop-outs included is not significant.
However, this is not a test of what any diet does. If people relapse when they stop taking the drug that controls a condition, we never take this as evidence that the drug is only effective in the short term.
A further consideration is, that outside of the diet trial, the mean weight of this population would likely have increased.
Yet another consideration is that the LCHF diets in most studies are ad lib (no conscious attempt made to count calories or to undereat), whereas the low-fat diets require restricting calories, presumably because they would not be effective otherwise.
This difference can be extrapolated to the real world, where diets are usually eaten ad lib, to explain the rise in obesity following the introduction of novel advice to restrict dietary fat and government campaigns to increase production of low-fat food products.[2]
[1] Feinman R. Intention-to-treat. What is the question? Nutrition & Metabolism20096:1
DOI: 10.1186/1743-7075-6-1 https://nutritionandmetabolism.biomedcentral.com/articles/10.1186/1743-7...
[2] Ludwig DS. Lowering the Bar on the Low-Fat Diet. JAMA. Published online September 28, 2016. doi:10.1001/jama.2016.15473
http://jamanetwork.com/journals/jama/fullarticle/2564564
Competing interests: No competing interests