Intermittent fasting (IF) is a proven weight-loss strategy, but the evidence for other benefits is mixed.

One such claim is increased longevity.

The most persuasive evidence suggests that if IF does help you live longer, it’s when the fasting is periodic and not absolute. This means that for a short period you eat a very small number of calories rather than none at all.

One version of IF involves eating just one meal a day.

Overall, you eat fewer calories than you might otherwise when consuming three meals a day. Which sounds good. But it may not be good for you.

A new study

Analysing data from more than 24,000 American adults 40 years of age and older, researchers asked interesting questions about the consequences of regularly skipping different meals.

They also looked at the association between health and intervals between meals.

In a new paper, the researchers found that “eating only one meal per day is associated with an increased risk of mortality in adults 40 years old and older”.

Other findings include:

• Skipping breakfast is associated with a higher risk of cardiovascular disease mortality
• Missing lunch or dinner carries a higher risk of all-cause mortality
• Among individuals who eat three meals daily, eating two adjacent meals less than or equal to 4.5 hours apart is associated with a higher all-cause death risk. In other words, you’re better off putting more than 4.5 hours between meals.

Not just relevant to intermittent fasters

The study isn’t just relevant to intermittent fasters, who are consciously restricting meals to lose weight.

The study found that about 40 per cent of study participants regularly ate fewer than three meals a day.

These participants were more likely to be: Younger; male; having less education and lower family incomes; smokers; drinking more alcohol;  food insecure; eating less nutritious food; having more snacks, and having less energy intake overall.

But even when adjusting for these lifestyle and dietary factors, the findings held up. In other words, they were as relevant to well-off people following a fad diet as those who couldn’t afford three meals a day.

The researchers recommend people eat at least two to three meals spread throughout the day.

In other words, if you want to engage in intermittent fasting, then eat no fewer than two meals a day.

What the researchers say

Lead author Dr Yangbo Sun is a researcher with the Department of Preventive Medicine, the University of Tennessee Health Science Centre.

She said: “At a time when intermittent fasting is widely touted as a solution for weight loss, metabolic health and disease prevention, our study is important for the large segment of American adults who eat fewer than three meals each day.

“Our research revealed that individuals eating only one meal a day are more likely to die than those who had more daily meals.”

The study’s senior investigator was Dr Wei Bao, an assistant professor in the Department of Epidemiology, College of Public Health, University of Iowa.

He said: “Our results are significant even after adjustments for dietary and lifestyle factors … and food insecurity.

“Our findings are based on observations drawn from public data and do not imply causality. Nonetheless, what we observed makes metabolic sense.”

Why one meal a day is so bad

Dr Bao said that “skipping meals usually means ingesting a larger energy load at one time”.

This can “aggravate the burden of glucose metabolism regulation and lead to subsequent metabolic deterioration”.

Dr Bao said this would explain the association between a shorter meal interval and mortality, as a shorter time between meals would result in a larger energy load in the given period.

The study data was drawn from participants in the National Health and Nutrition Examination Survey (NHANES) between 1999 and 2014.

NHANES collects health-related data to assess diet, nutritional status, general health, disease history and health behaviours every two years.