There has been considerable interest in an approach to eating that is usually described as ‘intermittent fasting’. This may involve restricting eating to a window of, say, 6 or 8 hours each day. It might involve alternating days of very restricted eating with ‘normal eating’. It might just skipping or delaying breakfast. The idea is that going without food for extended periods may have benefits for health and weight loss, in ways that go beyond mere calorie restriction.
I most recently wrote about intermittent fasting in humans for The Times newspaper in the UK, and you can read this piecehere. More recently, I wrote about a study in mice which appeared to lend some support for the concept of intermittent fasting. You can read this blog post here, but in short this study found that mice eating during an 8-hour window compared to those eating all day ended up lighter and with better functioning hormones such as insulin and leptin, despite consuming the same number of calories.
This week sees the publication of another mouse study that has some relevance to the concept of intermittent fasting . In this study, mice were fed in one or four ways:
- mice fed a high-fat diet in a scheduled way (set time for eating and set length of eating each day)
- mice fed a high-fat diet in an unscheduled (‘ad libitum’) way
- mice fed a low-fat diet in a scheduled way
- mice fed a low-fat diet in an unscheduled way
Over 18 weeks, all four groups of mice gained weight, but there were differences between the groups. The group coming off worst in terms of weight were those in group 2 (high-fat, unscheduled diet). Also, though, mice in group 1 ended up being 12 per cent lighter and had better functioning insulin compared to mice in group 4, despite consuming the same number of calories. This supports the idea that a calorie in not necessarily a calorie (different sources of calorie do not necessarily have the same effect on weight). However, groups 1 and 4 differed in two respects: both type of diet and schedule of feeding, and it’s impossible for this comparison to gauge which factor (or maybe both) was responsible for the differing results.
However, further insight here was gained by comparing groups 1 and 2 (same high-fat diet, different schedule of eating) which found that those in group 1 (compared to group 2) ended up 18 per cent lighter, and seemed to experience other benefits too such as dramatically reduced cholesterol levels as well as levels of the chief stress hormone cortisol.
I don’t have access to the full text of this article, but I note that here it is claimed:
…the mice on the scheduled high-fat diet exhibited a unique metabolic state in which the fats they ingested were not stored, but rather utilized for energy at times when no food was available, such as between meals.
Let’s not get too excited about this study, seeing that it was performed in mice and not men (or women). However, it does seems to provide some evidence to support the concept of intermittent fasting, perhaps combined with relatively high-fat eating. My experience in practice is that many individuals do very well on such an approach. While it may seem that they aren’t consuming much food, they are nor necessarily ‘underfed’ either, as perhaps these individuals are doing a good job of mobilising and metabolising their own fat (like the mice in the study). And this might also explain why such individuals may not complain of undue hunger either. After all, it’s possible that what they are not eating is being supplemented by the ‘food’ obtained from their own fat stores.
1. Sherman H, et al. Timed high-fat diet resets circadian metabolism and prevents obesity. The FASEB Journal 2012;26 8):3493