DIETERS focus on shedding the pounds - but more rarely on the long-term consequences of their diets.

New research published in The Lancet Public Health journal suggests that too little or too much carbohydrates is linked with higher risk of mortality, or early death. Moderate carbohydrates consumption had the lowest risk of mortality.

The US study goes further by looking at the type of foods which are used to make up the diet of people reducing carbohydrates.

Replacing carbohydrates with proteins and fats from plant foods instead of animal foods made a positive difference to longevity.

Co-author of the study, Professor Walter Willett, an expert in epidemiology and nutrition at Harvard T. H. Chan School of Public Health, 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.”

The scientists linked diet data from a large group of American citizens studied in the late 1980s and early 1990s to death records over the following 25 years.

This was then combined with data from other big studies, taking in consideration age, sex, ethnicity, total energy intake, education, exercise, income level, smoking, and diabetes.

The difference in life expectancy they calculated is sizeable. Those with very low carbohydrate consumption typically died four years earlier, while those on a very high carbohydrate diet lost one year off their life expectancy.

However, foods and dietary habits can change over time, and diet data collected from questionnaires can be imprecise, which might make the conclusions less reliable.

Low-carb diets have rapidly gained in popularity in Scotland and the UK, as they can help people lose weight as well as low-fat diets.

With two in three adults overweight or obese in Scotland, it is important to find diet strategies that work and sustain healthy ageing.

The new study emphasises moderation for carbohydrates intake, toward a “sweet spot” sustaining longevity, and the importance of plant foods.

Even now, Scots are still between one and two portions away from the five-a-day fruit and vegetables target.