The diet debate: are more fats or carbohydrates healthier?

Global perspectives on the nutritional value of carbohydrates and fats need to be reconsidered, according to the Prospective Urban-Rural Epidemiology (PURE) study.

Published in The Lancet, the study looked at the diet of 135,335 individuals from 18 low-, middle- and high-income countries, and analysed the consumption of carbohydrates, total fats and types of fat. Researchers then compared these diets to cardiovascular (CV) problems and mortality using questionnaires.

They found that high carbohydrate intake is linked to higher mortality rates and non-CV mortality compared to a high fat intake. Researchers therefore disagreed with the belief that total fat intake should be limited to less than 30% of a person’s energy.

“Limiting total fat consumption is unlikely to improve health in populations, and a total fat intake of about 35% of energy with concomitant lowering of carbohydrate intake may lower risk of total mortality. In fact, individuals with high carbohydrate intake, above 60% of energy, may benefit from a reduction in carbohydrate intake and increase in the consumption of fats,” explained Dr Mahshid Dehghan from the Population Health Research Institute, McMaster University.

After following the participants’ health for an average of seven years, they found that those with the highest intake of dietary fat, consisting of 35% of their daily calories, were 23% less likely to have died during the study period than those whose fat intake only accounted for about 10% of their daily calories.

The high-fat diets were also linked to an 18% reduced risk of stroke, and all three different types of fat — saturated, mono-unsaturated and polyunsaturated — were associated with 14–20% lower mortality rates.

Although a high intake of carbohydrates (around 77%) was associated with a higher risk of death, the risk of CV events did not change.

“For decades, dietary guidelines have focused on reducing total fat and saturated fatty acid (SFA) intake based on the presumption that replacing SFA with carbohydrate and unsaturated fats will lower LDL-C [‘bad’ cholesterol] and should therefore reduce CVD events,” Dehghan said.

However, Dehghan was careful to highlight that this evidence focuses on Western populations where there is a nutritional excess.

“PURE provides a unique opportunity to study the impact of diet on total mortality and CVD in diverse settings, some settings where over-nutrition is common and others where under-nutrition is of greater concern,” she said.

Overall, researchers concluded that the best diets include about 50–55% carbohydrates and around 35% total fat, including saturated and unsaturated. PURE co-author Dr Andrew Mente suggested more fruits, vegetables and legumes reduces the risk of mortality, but this does not need to exceed three to four servings a day.

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