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Oct 07, 2019

Questioning the Long-Term Safety of the High-Fat, Low-Carb Diet

A review of 10 studies finds a link between mortality risk and diets highest in protein and fat. 

Experts suggest rethinking recommendations for a low-carb diet, based on a recent study that tied low carbohydrate intake to increased risk of death from heart disease, cancer and all causes.

Published in the European Heart Journal, this study explored the long-term safety of a low-carb diet. It included data from a national survey study called NHANES (National Health and Nutrition Examination Survey), as well as nine other studies that tracked the health and lifestyle of U.S. adults. All studies assessed participants’ diets upon enrollment and then tracked survival for up to 29 years.

Analysis of NHANES, which included 24,825 American adults, tied a low-carb diet to 32% greater risk of death from all causes and 50–51% higher risk of death from stroke and heart disease. It also linked low carbohydrate intake to 36% greater risk of death from cancer.

A second analysis, which included 462,934 participants from nine different studies, linked low carbohydrate intake to 22% greater risk of death from all causes, 13% greater risk of heart-related death, and 8% greater risk of death from cancer.

NHANES included survey data from 1999–2010 and followed participants for an average of six years, while the pooled data had an average follow-up of 16 years.

For both analyses, researchers looked at the breakdown of protein, fat and carbohydrate intake in participants’ diets. Those with the highest ratio of protein and fat to carbohydrates were in the “low carb” group and were compared to participants with the highest intake of carbohydrates and lowest intake of protein and fat.

Authors note that in the NHANES analysis, the association between low-carb diets and mortality risk was strongest among non-obese participants. That means a low-carb diet could be more harmful in adults who are a healthy weight, especially over a long period of time.

It’s important to note that neither analysis can prove cause and effect, since none of the studies were randomized clinical trials. However, findings do add to concerns about the long-term effects of a low-carb diet on overall health.

According to authors, many studies have linked low-carb diets to weight loss—which in general is beneficial to health and quality of life. However, studies have questioned the long-term safety of low-carb diets over an extended period of time. Experts worry about the impact of a low-carb diet after achieving weight loss. That’s because low-carb diets tend to include higher amounts of fat, which can clog the arteries and lead to heart disease—the leading killer of men and women in the United States.

As a next step, authors encourage future research to explore the long-term health impact of low-carb diets and help inform future dietary recommendations.

Questions for You to Consider

  • What is a heart-healthy diet?

  • A heart-healthy diet is full of fruits, vegetables, beans and whole grains and includes low-fat dairy, fish and nuts as part of a balanced diet. It’s important to limit intake of added sugars, salt (sodium) and bad fats (saturated and trans fats).

  • What is a healthy weight for me?
  • A few important tools can be used to determine if an individual is underweight, normal weight or overweight. The easiest tool is a Body Mass Index, which is calculated using height and weight to estimate levels of body fat. However, Body Mass Index is not always accurate, particularly among individuals with extremely high or low amounts of muscle. In these cases, measuring waist circumference is helpful in assessing weight, as a waist circumference greater than 35 inches for a woman or 40 inches for a man is considered unhealthy.

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