Bad News for Keto? Low-Carb Diets Linked to Increased Mortality

An Arivale Hot Topic

Niha Zubair, Arivale Clinical Research Scientist, PhD
Niha Zubair
Arivale Clinical Research Scientist, PhD

If you’re trying to lose weight, you may try a diet that limits certain foods or particular nutrients. But, how those types of diets can affect your long-term health is not well studied. One oft-limited nutrient currently under scrutiny is carbohydrates.

Low-carb diets, such as the keto diet, are extremely popular, with purported benefits including weight loss, increased clarity, or improved glycemic markers. Conversely, some diets claim health benefits can be achieved by eating less fat and more carbs.

It’s unclear how diets varying in carbohydrate content could affect health in the long run. Studies have reported conflicting results: some show an increased risk of mortality from low-carb diets, while others show it’s high-carb diets that are increasing your risk of death.

However, most studies have reported mortality risk based on groupings of carbohydrate intake that are relative to the populations being studied, which may partially account for the differences in findings. For example, “low carbohydrate” intake in an Asian population may be equivalent to “high carbohydrate” intake in a European population – both of which are shown to be protective against mortality.

Another issue that could contribute to these mixed findings is that most of these studies have not accounted for the effects of fat and protein sources (i.e. animal-based vs. plant-based) used to replace carbohydrates in a low-carb diet.

The Study

To address these gaps, a new study published last month in the Lancet and covered by CNN examined a cohort of over 15,000 individuals between 45 and 64 years old over a median of 25 years to assess the effect of carbohydrate intake – and sources of fat and protein – on mortality in the Atherosclerosis Risk in Communities Cohort (ARIC), which is comprised of four US communities from diverse socioeconomic backgrounds.

This analysis accounted for potential factors that may influence the results, such as: demographics, daily energy intake, study center, education, exercise, income level, cigarette smoking, and diabetes. They then contextualized these findings in a meta-analysis of 400,000 individuals, combining this data with those from other multinational cohorts.

In both ARIC and the meta-analysis, researchers found diets that got over 70 percent or under 40 percent of their energy from carbohydrates were associated with increased mortality. The lowest risk of mortality was observed in diets that got between 50 percent and 55 percent of their energy from carbs, which is very close to what most nutritionists would call a high-carb diet.

To put this in rough perspective, the average woman needs about 2,000 kcals per day. Thus, a diet with carbohydrate intake greater than 1,400 kcals or less than 800 kcals would put her at a higher risk for death. The most ideal carbohydrate intake in terms of lowering her risk of death would be 1,000-1,100 kcals per dayFor context, a ketogenic diet containing between 20 grams and 50 grams of carbohydrates per day contains 80 kcal to 200 kcal from carbs.

Interestingly, researchers found that low-carb diets that replaced carbohydrates with animal-based fat or protein were associated with a greater mortality risk, whereas low-carb diets that replaced carbohydrates with plant-based fat or protein were associated with a decreased mortality risk

Researchers say their results provide further evidence that animal-based, low-carb diets – such as many popular ketogenic diets – should be discouraged and that if carbohydrate restriction is chosen, replacing carbohydrates with primarily plant-based fats and proteins could be considered as a long-term approach to promote healthy aging.

Arivale’s Take

While this study was published in a renowned journal, it isn’t without limitations, some of which we describe here.

First, the study is based on observational data and cannot conclusively prove that high or low-carb diets increase mortality, only that there may be a correlation.

Second, collecting data on diet is difficult! Even remembering what you ate yesterday can be a challenge, which means there is bound to be some measurement or recall error by participants.  Furthermore, diet was assessed at two time points in the beginning of the study, spanning a six-year period. So, researchers may bucket an individual as eating a low-carb diet based on measurements from the first six years, but for the remainder of the study the individual may have switched to a higher-carb diet.

Third, researchers could not disentangle animal sources of fat and protein. For example, beef, pork, chicken, and fish were all considered equal, when in reality some might be more or less health-protective than others. Similarly, the study focused on general carbohydrate intake and didn’t distinguish refined or whole-grain sources of carbohydrates, which likely affect health differently.

Regardless, the study reinforces that fad or extreme diets may not be best for our overall health in the long term. These findings are aligned with Arivale’s philosophy of eating a mostly plant-based, minimally processed diet consisting primarily of whole, fresh foods.

Further Reading

[Arivale Hot Topics address health stories currently in the news. The Arivale Clinical Team’s commentary on these news articles is not a review of the scientific evidence, nor an endorsement of a specific study, and is not meant as official medical opinion.]