Question: I try to stay active and eat well. I’ve followed Dr Michael Mosley’s advice on intermittent fasting and time-restricted eating to improve my health. However, I recently read of research linking intermittent fasting to cardiovascular problems. What is the latest advice?
Answer: Intermittent fasting is promoted as a way to lose weight, improve your heart and brain health and possibly live longer. The first problem here is that it assumes losing weight is possible and automatically improves health. Second, as Listener columnist Jane Clifton notes (April 27), preliminary research presented to the American Heart Association has linked certain types of intermittent fasting to a 91% higher risk of cardiovascular death (you can read Clifton’s story here).
So, what does this mean in practice? Intermittent fasting is an eating pattern that alternates between periods of fasting and eating. Typical methods involve either set hours of fasting each day, for example, a 12-16 hour fast daily or fasting for 24 hours, twice weekly.
Clinical trials have found that certain types of time-restricted eating improve several cardiometabolic health measures in the short term, such as blood pressure, blood glucose and cholesterol levels.
However, little research has looked at the long-term effects. Further, intermittent fasting proponents have assumed many things, such as that long-term weight loss is desirable and possible (more on that later).
Then there are the assumptions that the short-term cardiovascular benefits observed with intermittent fasting can result in improved long-term brain and cardiovascular health and potentially increase longevity.
All these touted benefits have been called into question by research led by Victor Wenze Zhong, of Shanghai Jiao Tong University, unveiled in Chicago in March. It found people who ate all their food within an 8-hour window daily had that near-doubling of risk of death due to cardiovascular disease.
The study used dietary data from 20,000 participants in the annual US National Health and Nutrition Examination Surveys from 2003-18, as well as data on deaths in the US from 2003-19.
It also found people with existing cardiovascular disease who had a daily eating window of 8-10 hours had a 66% higher risk of death from heart disease or stroke.
On the other hand, cancer patients with an eating window of 16 hours or more (avoiding intermittent fasting practices) had improved longevity. Unsurprisingly, time-restricted eating was not associated with a reduction in the risk of death.
The research has not yet been published in a scientific journal. Without the full study details, we do not know if other factors could be implicated: for example, did the people who followed an intermittent fasting diet have poorer nutritional intakes, which might explain their poorer health outcomes? Although this observational study cannot prove that intermittent fasting caused increased cardiovascular risks, it certainly suggests caution is warranted – particularly for people with existing health conditions.
Furthermore, the belief that intermittent fasting will produce weight loss, and thus better health, is flawed. Contrary to popular opinion, body weight is not a proxy for health, so losing weight does not automatically make one healthier. For instance, a 2021 review in the journal iScience noted any health risks associated with obesity are largely reduced or eliminated by moderate-to-high physical activity levels. In other words, evidence suggests behaviour change, rather than weight loss as such, benefits health and wellbeing.
There is little risk and much to gain from adopting a traditional Mediterranean lifestyle instead of intermittent fasting or similar dietary patterns. The superior cardiovascular health and longevity of traditional Mediterranean populations was attributed to their active lifestyle and predominantly plant-based diets, containing plenty of fruits, vegetables, legumes, nuts, olive oil and wholegrains, a moderate intake of fish and poultry, and a low intake of dairy products, red meat, processed meats and sweets.
They also drank wine in moderation with their meals. Rather than following an eating pattern of dubious benefit, why not enjoy a tasty diet linked to better health and wellbeing?
