The medical journal The Lancet produced a study in August 2018(Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis) that examined how the proportion of carbohydrates in the diet affected life expectancy.
The background was this: if you are on a “low carb diet,” in which you cut out most or all carbohydrates, that means you eat more proteins and fats to get to your daily energy intake. The long-term effect of low carbohydrate intake in terms of mortality is controversial and depends on whether one eats animal or plant proteins und fats instead. Therefore, the researchers from the Lancet study investigated how the relationship between carbohydrate intake and mortality was.
On the one hand, data were reviewed from an American study (ARIC) in which 15 428 adults aged 45-64 years had completed a questionnaire on carbohydrate intake. This was done over a follow-up period of 25 years. On the other hand, other studies (also on carbohydrate intake) from several countries were examined.
The result: a higher risk of mortality was found for both low (below 40% of energy requirements) and high (above 70%) carbohydrate intake. The risk of death was lowest in those subjects who had an average carbohydrate intake of 50-55%. In addition, mortality increased when carbohydrates were replaced with animal proteins and fats (beef, pork, lamb, or chicken) and decreased when proteins were of plant origin (vegetables, nuts, peanut butter, and whole grain bread).
As for the proportion of carbohydrates in the diet, we can therefore conclude that of the energy intake per day – here everyone has an individual need – the proportion of carbohydrates should be about 50-55%. We can also read this at the German and Swiss Societies for Nutrition. Eating too little or too many carbohydrates over a long period of time can translate into a higher risk of mortality.  Above all, a varied and wholesome diet is important to obtain vital nutrients.