According to a new prospective cohort study and meta-analysis, published 16 August 2018 in the journal The Lancet Public Health, advocates of both very high and very low carbohydrate diets are wrong about which approach is best for health.
The aim of the paper was to assess “whether the substitution of animal or plant sources of fat and protein for carbohydrate affected mortality”.
“We studied 15,428 adults aged 45–64 years, in four US communities, who completed a dietary questionnaire at enrollment in the Atherosclerosis Risk in Communities (ARIC) study (between 1987 and 1989),” wrote the authors.
To further examine the associations between carbohydrate intake and all-cause mortality, the researchers also conducted a meta-analysis, which combined the data from the ARIC, as well as from seven other prospective multi-national studies.
After 25 years of tracking their subjects' health and eating habits, the authors found that diets composed of 50-55% carbohydrates were the most conducive to hefty lifespans, as compared to diet patterns characterised by very low (<40%) and very high (>70%) amounts of carbohydrates.
Those favouring high-carb (up to 70%) diets were found to have lifespans up to a year shorter than the 50-55% carb group, while those with 30-40% of carbs in their diets lost about 2.3 years.
Worst of all, people who eat very low-carb (<30%) diets lived as many as 4 years shorter, compared to the moderate carb group.
Another key finding was that replacing some of the carbs with plant-derived fats and proteins did not have the same negative effect – people eating diets low in carbohydrates, but high in plant fats and proteins actually came out on top in terms of longevity.
“Results varied by the source of macro-nutrients: mortality increased when carbohydrates were exchanged for animal-derived fat or protein (1·18, 1·08–1·29) and mortality decreased when the substitutions were plant-based (0·82, 0·78–0·87)”.
Despite the limitations – namely, self-reported carb intakes and the observational nature of the study – the overall study design was recognised as robust by many researchers who were not involved in the research.
So if you want to go low-carb, make sure to replace at least some of the animal-derived fats and proteins with those of plant origin.