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Moderate Carbohydrate Intake May be Best for Health
A new study has found that diets both low and high in carbohydrates were linked with an increase in mortality, while moderate consumers of carbohydrates had the lowest risk of mortality.
Moderate carbohydrate intake may be best for health. Image credit: US Department of Agriculture
The study also found that low-carb diets that replace carbohydrates with proteins and fats from plant sources were associated with lower risk of mortality compared to those that replace carbohydrates with proteins and fat from animal sources.
Diets both low (less than 40% energy) and high (more than 70% energy) in carbohydrates were linked with an increase in mortality, while moderate consumers of carbohydrates (50-55% of energy) had the lowest risk of mortality.
The primary findings also suggest that not all low-carbohydrate diets appear equal -- eating more animal-based proteins and fats from foods like beef, lamb, pork, chicken and cheese instead of carbohydrate was associated with a greater risk of mortality.
Alternatively, eating more plant-based proteins and fats from foods such as vegetables, legumes, and nuts was linked to lower mortality.
Previous randomised trials have shown low carbohydrate diets are beneficial for short-term weight loss and improve cardiometabolic risk. However, the long-term impact of carbohydrate restriction on mortality is controversial with prospective research so far producing conflicting results. What's more, earlier studies have not addressed the source or quality of proteins and fats consumed in low-carb diets.
To address this uncertainty, researchers assessed the association between overall carbohydrate intake (categorised by quantiles) and all cause-mortality after adjusting for age, sex, race, total energy intake, education, exercise, income level, smoking, and diabetes.
Results showed a U-shape association between overall carbohydrate intake and life expectancy, with low (less than 40% of calories from carbohydrates) and high (more than 70%) intake of carbohydrates associated with a higher risk of mortality compared with moderate intake (50-55% of calories).
The researchers estimated that from age 50, the average life expectancy was an additional 33 years for those with moderate carbohydrate intake -- 4 years longer than those with very low carbohydrate consumption (29 years), and 1 year longer compared to those with high carbohydrate consumption (32 years).
However, the authors highlight that since diets were only measured at the start of the trial and 6 years later, dietary patterns could change over 25 years, which might make the reported effect of carbohydrate consumption on lifespan less certain.
In the next step of the study, the authors revealed similar trends, with participants whose overall diets were high and low in carbohydrates having a shorter life expectancy than those with moderate consumption.
In further analyses examining whether the source of proteins and fats favoured in low-carbohydrate diets -- plant-based or animal-based -- was associated with length of life, researchers found that replacing carbohydrates with protein and fat from animal sources was associated with a higher risk of mortality than moderate carbohydrate intake.
In contrast, replacing carbohydrates with plant-based foods was linked to a lower risk of mortality.
The findings show observational associations rather than cause and effect. Considering evidence from other studies, the authors speculate that Western-type diets that heavily restrict carbohydrates often result in lower intake of vegetables, fruit, and grains and lead to greater consumption of animal proteins and fats -- some of which have been implicated in stimulating inflammatory pathways, biological aging, and oxidative stress -- and could be a contributing factor to the increased risk of mortality.
Whilst high carbohydrate diets (common in Asian and less economically advantaged nations) tend to be high in refined carbohydrates such as white rice, may also contribute to a chronically high glycaemic load and worse metabolic outcomes.
Based on first principles, a U-shaped association is logical between most essential nutrients versus health outcomes. Essential nutrients should be consumed above a minimal level to avoid deficiency and below a maximal level to avoid toxicity. This approach maintains physiological processes and health (ie, a so-called sweet spot).
Although carbohydrates are technically not an essential nutrient (unlike protein and fats), a certain amount is probably required to meet short-term energy demands during physical activity and to maintain fat and protein intakes within their respective sweet spots.
On the basis of these principles, moderate intake of carbohydrate (eg, roughly 50% of energy) is likely to be more appropriate for the general population than are very low or very high intakes. (Tasnim News Agency)
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