The low carbohydrate (ketogenic) diet is currently a very popular weight loss diet.
Recently the diet’s safety has been questioned by some investigators.
Resources (1) and (2) are very recent articles that address this issue. Resource (3) is press release based on Resource (2) which has only the abstract currently available.
When the full text of Resource (2) becomes available I will review it along with Resource (1).
Reviewing Resource (1) reveals the following from the Summary:
Findings
During a median follow-up of 25 years there were 6283 deaths in the ARIC cohort, and there were 40 181 deaths across all cohort studies. In the ARIC cohort, after multivariable adjustment, there was a U-shaped association between the percentage of energy consumed from carbohydrate (mean 48·9%, SD 9·4) and mortality: a percentage of 50–55% energy from carbohydrate was associated with the lowest risk of mortality. In the meta-analysis of all cohorts (432 179 participants), both low carbohydrate consumption (<40%) and high carbohydrate consumption (>70%) conferred greater mortality risk than did moderate intake, which was consistent with a U-shaped association (pooled hazard ratio 1·20, 95% CI 1·09–1·32 for low carbohydrate consumption; 1·23, 1·11–1·36 for high carbohydrate consumption). However, results varied by the source of macronutrients: mortality increased when carbohydrates were exchanged for animal-derived fat or protein (1·18, 1·08–1·29) and mortality decreased when the substitutions were plant-based (0·82, 0·78–0·87).
Interpretation
Both high and low percentages of carbohydrate diets were associated with increased mortality, with minimal risk observed at 50–55% carbohydrate intake. Low carbohydrate dietary patterns favouring animal-derived protein and fat sources, from sources such as lamb, beef, pork, and chicken, were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality, suggesting that the source of food notably modifies the association between carbohydrate intake and mortality.
Resources:
(1) Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis [Full Text HTML] [Full Text PDF]. Open Access Published:August 16, 2018DOI:https://doi.org/10.1016/S2468-2667(18)30135-X
(2) Low-carbohydrate diets and all-cause and cause-specific mortality: a population-based cohort study and pooling prospective studies. Here is a link to the abstract. The article is not yet available online. The abstract was presented at the ESC Congress 2018.
(3) This press release is based on Resource (2) above: Low carbohydrate diets are unsafe and should be avoided 28 Aug 2018, from ESC Congress 2018.
Topic(s): Risk Factors and PreventionObesity
Munich, Germany – 28 Aug 2018: Low carbohydrate diets are unsafe and should be avoided, according to a large study presented today at ESC Congress 2018. (1)Study author Professor Maciej Banach, of the Medical University of Lodz, Poland, said: “We found that people who consumed a low carbohydrate diet were at greater risk of premature death. Risks were also increased for individual causes of death including coronary heart disease, stroke, and cancer. These diets should be avoided.”
Obesity is a major health issue worldwide and raises the risk of several chronic conditions, including cardiovascular disease, hypertension, type 2 diabetes, and cancer. Different diets have been suggested for weight loss, such as diets low in carbohydrates and high in protein and fat. The long-term safety of these diets is controversial, with previous studies reporting conflicting results of their influence on the risk of cardiovascular disease, cancer, and death.
This study prospectively examined the relationship between low carbohydrate diets, all-cause death, and deaths from coronary heart disease, cerebrovascular disease (including stroke), and cancer in a nationally representative sample of 24,825 participants of the US National Health and Nutrition Examination Survey (NHANES) during 1999 to 2010. Compared to participants with the highest carbohydrate consumption, those with the lowest intake had a 32% higher risk of all-cause death over an average 6.4-year follow-up. In addition, risks of death from coronary heart disease, cerebrovascular disease, and cancer were increased by 51%, 50%, and 35%, respectively.
The results were confirmed in a meta-analysis of seven prospective cohort studies with 447,506 participants and an average follow-up 15.6 years, which found 15%, 13%, and 8% increased risks in total, cardiovascular, and cancer mortality with low (compared to high) carbohydrate diets (see figure for total mortality).
Professor Banach said: “Low carbohydrate diets might be useful in the short term to lose weight, lower blood pressure, and improve blood glucose control, but our study suggests that in the long-term they are linked with an increased risk of death from any cause, and deaths due to cardiovascular disease, cerebrovascular disease, and cancer.”
Participants in the NHANES study had an average age of 47.6 years, and 51% were women. They were divided into quartiles based on the usual percentage of carbohydrates in their diet. The risks of all-cause and cause-specific death over an average 6.4-year follow-up rose with each fall in carbohydrate intake (see table), and remained significant after adjusting for all available factors that might have influenced the association (model 2 in the table).
The researchers also examined the link between all-cause death and low carbohydrate diets for obese (body mass index [BMI] 30 kg/m2 or greater) and non-obese (BMI under 30 kg/m2) participants in two age groups (55 years and older versus under 55) and found that the link was strongest in the non-obese older participants.
Regarding the mechanisms underlying the correlation between low carbohydrate diets and death, Professor Banach noted that animal protein, and specifically red and processed meat, has already been linked with an increased risk of cancer. He said: “The reduced intake of fibre and fruits and increased intake of animal protein, cholesterol, and saturated fat with these diets may play a role. Differences in minerals, vitamins and phytochemicals might also be involved.”
He concluded: “Our study highlights an unfavourable association between low carbohydrate diets and total and cause-specific death, based on individual data and pooled results of previous studies. The findings suggest that low carbohydrate diets are unsafe and should not be recommended.”
