What Research Says about the 5:2 Diet
Periods of fasting are a natural condition. When humans lived as hunters and gatherers they probably experienced long periods of “semi-starvation,” and many researchers think that our bodies are adapted to this. Sure enough, limited intake of calories has been shown to have good effects in animal studies. It reduces inflammation and stimulates expression of genes that protect against cardiovascular disease, diabetes and cancer.1
Detailed studies of people are lacking, however, although it is known that cases of diabetes and cardiovascular disease were reduced in connection with food rationing during the Second World War.
Less cardiovascular disease and increased life span have also been seen on the Japanese island of Okinawa and other places where people traditionally consumed fewer calories.
However, these are observations — not controlled experiments — and many other factors may therefore have an influence.
Studies Are Lacking about the Effects of Calorie Restriction
One of the few experiments that has been conducted is a Swedish study that showed weight loss of 7-9 kg among those who completed a two-year program with calorie restriction. The problem was that only 35% of the participants were able to maintain this diet during the entire two-year period. Studies are still lacking on how calorie restriction affects health in people long-term.2
What Does Research Say about the 5:2 Diet?
A modern variation of calorie restriction is the 5:2 diet, which has been extremely popular since it was promoted by the journalist Michael Mosley on BBC in 2012.3 It exists in several variations, the basis of which is that you radically reduce your calorie intake two days per week.
The problem is that there are no extensive studies that have investigated the effect of 5:2 in people, even though some maintain that the diet is “scientifically based.”1 Basically only rat studies have been done. And we know how difficult it is to translate rat studies to people.
In theory 5:2 should be good, even if scientific support is lacking. It can also be beneficial to learn to recognize hunger and realize that it is not dangerous to be hungry during some periods.
Please note that the 5:2 diet may be dangerous if you have insulin-treated diabetes, because the risk of low blood sugar increases with fasting.
Find a Sustainable Solution for You
The question is whether the 5:2 diet is sustainable long-term. It is one thing that Michael Mosley sticks to 5:2 for three months while the TV cameras are on. It is another thing altogether to maintain this dietary pattern year in and year out.
Some people can perhaps succeed in sticking to this pattern year after year. But in many cases it seems easier to be extreme for a short time than moderate over a long period of time.
Some who truly live with long-term moderation are the residents of Okinawa in Japan. Their proverb, Hara hachi bu, means that you eat until you are roughly 80% full every day. In total this entails approximately as many calories as 5:2, but without the extreme fluctuations, whose effects on the body are still not investigated.
Sometimes trendy diets and spectacular new habits aren’t necessary. Traditional moderation on an everyday basis is probably at least as healthy.
How can you live more moderately?
1. Måns Rosén. Truth about food and health: what does research say? [In Swedish: Sanningen om mat och hälsa: vad säger forskningen?]
2. Lantz H et al., J Intern Med 2003;253:463
3. Mosley, M et al., 5:2 diet.