Reducing carbohydrate intake is the most effective way to diet for weight loss, according to a review article by the Mayo Clinic in the US.
The researchers, writing in the Journal of the American Osteopathic Association, looked at 72 high-quality studies published between 2005 and 2016.
They found that, over the course of six months, people lost up to nine pounds more on a low-carb diet than those on a low-fat diet.
However, the difference between the diets diminished after one or two years. (But see our analysis below.)
The study did not address whether the weight lost was in muscle, water, or fat, and mostly relied on self-reported data provided by participants.
Dr Heather Fields, the study’s lead author, said: ‘The best conclusion to draw is that adhering to a short-term low-carb diet appears to be safe and may be associated with weight reduction.
‘However, that weight loss is small and of questionable clinical significance in comparison to low-fat diets. We encourage patients to eat real food and avoid highly processed foods, especially processed meats, such as bacon, sausage, deli meats, hot dogs, and ham when following any particular diet.’
A Daily Mail report on the study said that low-carb diets could be ‘dangerous’ in the long-term. However, the study merely reported a lack of data on the subject.
‘Our review found no safety issues identified in the current literature, but patients considering low-carb diets should be advised there is very little data on long-term safety and efficacy.’
The researchers say that although people who cut down on carbohydrates tend to consume more meat, which has been shown to increase cancer and all-cause mortality risk, this effect was not evident in those following the diet for six months.
This was a review article on the benefits of low-carbohydrate, high-fat (LCHF) diets.
The studies included were of higher-level evidence but of course not all randomised trials or systematic reviews are of the same quality. Perhaps a better way forward would have been a meta-analysis, which would have combined the results of all trials.
Weight loss superiority of LCHF diets was noted over others but the average difference in weight lost was small.
The effect on blood sugar was variable but evidence does exist for an improvement of blood sugar in those with type-2 diabetes.
The effect on blood lipid levels (cholesterol/triglycerides) of the LCHF diet was variable but usually positive. Those trials that showed discordant results were possibly compromised in some cases if patients used vegetable oils. These fats can be converted into transfats, which raise cholesterol, and their impact is often masked by the presence of saturated fat in the diet (does not raise cholesterol)
There is nothing in the literature that suggests that a LCHF diet is injurious or harmful to health. Indeed, there is a lot of evidence suggesting that there may be a benefit to keeping overall carbohydrate ingestion low that could be harnessed as a potential preventative measure in certain cancers. Evidence, both indirect (lab studies) and theoretical, suggests that there may be a role to play for LCHF diets in preventing recurrences of certain cancers. This research is ongoing.
LCHF diets can ameliorate the side effects of radiotherapy in cancer treatment and have a role, both historical but also current, in the treatment of epilepsy, particularly in patients with the more severe form. These roles were not mentioned in the article.
By focusing on ‘gold standard’ levels of evidence we often neglect the promise of other therapies just because a trial meeting the level of evidence required simply hasn’t been done.