Cutting back on carbs helps people live longer – as long as you don’t replace them with meat, according to a new study.
Researchers found that eating carbohydrates in moderation seems to be “optimal” for health and longevity.
But the study, published in The Lancet Public Health journal, also suggests that low carb diets that replace carbs with meat – such as the Atkins Diet – actually make people more likely to die young.
The findings show that low-carb diets that replace carbs with proteins and fats from plant sources are associated with a lower risk of dying compared to those that replace carbs with proteins and fat from animal sources.
The study involving more than 15,400 people in the United States found that diets both low and high in carbs were linked with an increase in mortality, while moderate consumers of carbs – classed as 50 to 55 per cent of calorie intake – had the lowest risk of mortality.
The main findings, confirmed in an analysis of studies on carbohydrate intake including more than 432,000 people from over 20 countries, also suggest that not all low-carb diets appear equal.
Eating more animal-based proteins and fats from foods such as beef, lamb, pork, chicken and cheese instead of carbs was associated with a greater risk of dying.
But eating more plant-based proteins and fats from foods such as vegetables, legumes, and nuts was linked to lower mortality.
Study leader Dr Sara Seidelmann, of Brigham and Women’s Hospital in the US, said: “We need to look really carefully at what are the healthy compounds in diets that provide protection.
“Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight loss strategy.
“However, our data suggests that animal-based low carbohydrate diets, which are prevalent in North America and Europe, might be associated with shorter overall life span and should be discouraged.
“Instead, if one chooses to follow a low carbohydrate diet, then exchanging carbohydrates for more plant-based fats and proteins might actually promote healthy ageing in the long term.”
Previous trials have shown low carb 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 research so far producing conflicting results.
Earlier studies didn’t address the source or quality of proteins and fats consumed in low-carb diets.
To address the uncertainty, researchers began by studying 15,428 adults aged 45 to 64 from diverse socio-economic backgrounds from four US communities.
At the start of the study and again six years later, participants completed a dietary questionnaire on the types of food and drinks they consumed, what portion size and how often, which the researchers used to estimate the cumulative average of calories they derived from carbs, fats, and protein.
The researchers assessed the association between overall carb intake and all cause-mortality after adjusting for age, sex, race, total energy intake, education, exercise, income level, smoking, and diabetes.
The results showed low and high intake of carbs were associated with a higher risk of mortality, compared with moderate intake.
The researchers estimated that from age 50, the average life expectancy was an additional 33 years for those with moderate carb intake — four years longer than those with very low carb consumption, and one year longer compared to those with high carb consumption.
But the researchers pointed out that since diets were only measured at the start of the trial and six years later, dietary patterns could change over 25 years, which might make the reported effect of carbohydrate consumption on lifespan less certain.
The analysis of previous studies involving a total of 432,179 people in European, North American and Asian countries revealed similar trends, with participants whose overall diets were high and low in carbs having a shorter life expectancy than those with moderate consumption.
Dr Seidelmann said: “A mid-range of carbohydrate intake might be considered moderate in North America and Europe where average consumption is about 50 per cent but low in other regions, such as Asia, where the average diet consists of over 60 per cent carbohydrates.”
Co-author Prof Walter Willett, of Harvard T. H. Chan School of Public Health in the Us, said: “These findings bring together several strands that have been controversial.
“Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein, and carbohydrate,”
Considering evidence from other studies, the research team believe that Western-type diets that heavily restrict carbs often result in lower intake of vegetables, fruit, and grains and lead to greater consumption of animal proteins and fats – and could be a contributing factor to the increased risk of mortality.
High carb diets – common in Asian and poorer countries – tend to be high in refined carbohydrates such as white rice, and may also contribute to a chronically high glycaemic load and worse metabolic outcomes.
Study senior author Prof Scott Solomon, of Harvard Medical School, added: “This work provides the most comprehensive study of carbohydrate intake that has been done to date, and helps us better understand the relationship between the specific components of diet and long term health.
“While a randomised trial has not been performed to compare the longer term effects of different types of low carbohydrate diets, these data suggest that shifting towards a more plant-based consumption is likely to help attenuate major morbid disease.”