Unhealthy low-carbohydrate and low-fat diets can increase long-term chronic illness such as cardiovascular disease and diabetes, although healthy low-carbohydrate and low-fat diets are associated with lower total mortality, according to study results published in JAMA Internal Medicine. The study results found that there is no association between overall low-carbohydrate and low-fat diets and total mortality.

To investigate this association, the investigators conducted a prospective cohort study using data from the US National Health and Nutrition Examination Survey. The main outcome measured all-cause mortality. The investigation included 37,233 adults aged 20 years and older (average age, 49.7 years; 52.6% women); 4866 deaths were reported in the 297,768 person-years of follow-up.

After multivariable adjustments, hazard ratios for total mortality per 20 percentile increase in dietary scores for unhealthy and healthy low-carbohydrate-diet scores were 1.07 and 0.91, respectively; adjusted hazard ratios for unhealthy and healthy low-fat-diet scores were 1.06 and 0.89, respectively.

The authors noted that the link between types of low-carbohydrate and low-fat diets and mortality could involve many possible mechanisms. “Fat provides more than twice as much energy as carbohydrates and protein by weight. A high-saturated-fat diet is highly palatable and may have a weak effect of satiation, potentially leading to overconsumption and obesity.”


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The investigators also noted that “low-quality carbohydrates, such as refined grains and added sugars, provide limited nutritional value, and their high glycemic load could be associated with high postprandial glucose and insulin, inflammation, insulin resistance, and dyslipidemia.”

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“The food sources of high-quality carbohydrates, plant protein, and unsaturated fat include whole grains, nonstarchy vegetables, whole fruits, and nuts. These foods and their bioactive components (such as fiber, vitamins and minerals, and phytochemicals), rather than the macronutrients, may be involved in the associations between healthy [low-carbohydrate diet] and [low-fat diet] scores and mortality,” they concluded.

Reference

Shan Z, Guo YG, Hu FB, Liu L, Qi Q. Association of low-carbohydrate and low-fat diets with mortality among US adults [published online January 21, 2020]. JAMA Intern Med. doi:10.1001/jamainternmed.2019.6980