There has been some recent interest, even in the mainstream media, in the practice of ‘intermittent fasting’. Essentially, this means going for extended periods of time without food. It comes in many different guises. Skipping of significantly delaying breakfast is one approach. Contracting the ‘window’ available for eating each day to, say, 6 or 8 hours is another approach. Still another is to alternate days of no food or very limited intake with days during which eating is unrestricted.
One of the theories about why intermittent fasting might have benefits concerns the hormone insulin. When we eat, insulin is generally secreted. This hormone helps sweep nutrients such as glucose (sugar) out of the bloodstream and into the body’s cells where it can be ‘burned’ for energy. Fat, in this scenario, is believed to less likely to be metabolised for energy. In the ‘fasted’ state, though, insulin levels are relatively low, and this might help fat-burning, as least in part because when insulin levels are low fat is more likely to be released from fat cells and be available for metabolism.
Theory dictates, therefore, that very regular eating might keep insulin levels chronically (persistently) elevated and increase our risk of running into weight issues. On the other hands, less frequent eating may count in our favour.
All the theory in the world does not really matter in the end, though, because if we want to be sure that reduced meal frequency is beneficial somehow it needs testing. Earlier this year Dutch scientists undertook an interesting study in which the effects of different meal frequencies were tested on a group of 12 healthy men .
On one occasion, the men were fed a diet (15 per cent protein, 30 per cent fat, 55 per cent carbohydrate) for 36 hours, with the food split into three meals a day. On another occasion the same food was eaten, but this time it was split into 14 portions each day. This second approach is certainly extreme and does not generally reflect what frequent eaters do in practice. However, sometimes in experiments it can make sense to use very different approaches (in this case 14 ‘meals’ versus 3) to maximise the chances of detecting some difference.
One of the things that the researchers measured was the ‘oxidation’ (metabolism) of fat and carbohydrate. They hypothesised that eating 3 meals a day might shift metabolism from sugar towards fat for the reasons discussed above. In this study, though, they did not see such a shift.
However, other differences were seen between the diets. Notably, the amount of sugar that appeared in the bloodstream was lower when the individuals were eating the 3-meal-a-day regime. This suggests that the lower meal frequency enjoyed better blood sugar control overall (a good thing), and something that the authors suggest may contribute to improved weight control over time.
But there’s more: the reduced eating frequency was also found to lead to improvements in the resting metabolic rate compared to the more frequent eating. This, in theory, may also assist weight control efforts in the longer term.
The other notable difference was that when eating 3 times a day (compared to eating 14 times a day), individuals were less hungry and felt more sated. The authors comment that:
The [different] responses between smaller and larger eating occasions may simply be due to the inability of the body to detect the size of a smaller eating occasion as an adequate physiological load, reducing or eliminating the eating related responses typically observed when larger eating occasions occur.
Or to put it another way, the small ‘meals’ were not big enough to properly satisfy the appetite.
Though interesting, this study has some limitations. It studied a relatively small group made up of healthy men. A larger group might have yielded more significant results. However, we may have got different results in women or individuals who are overweight/obese and more likely to be ‘metabolically deranged’ and therefore different that the individuals studied here. Nevertheless, the study is useful in that it provides at least some evidence which supports the idea that lower meal frequency may have benefits for individuals.
This study was not a test of intermittent fasting, but provides some evidence that challenges that are sometimes made that ‘little and often’ is the best way to eat. My experience is that those needing to eat this way are often foods that simply don’t sustain them very well perhaps because of their relatively low-protein, low-fat, and blood sugar disruptive nature. Examples include breakfast cereal, cereal bars, ‘healthy’ meal replacement bars and sandwiches.
What is the ideal frequency to eat? I think it depends on the individual and perhaps that individual’s circumstances. In general, though, I’d follow these two basic guidelines:
- don’t eat if you’re not hungry
- don’t allow yourself to get too hungry before you eat
The thinking behind point 2 is that if people get very hungry, they find it harder to eat healthily.
When I started experimenting with intermittent fasting a year or so ago, it occurred to me that my previous beliefs about our ‘need’ to eat three times a day were just wide of the mark for me and, as it turns out, a lot of other people now. I now encourage a much more fluid approach based on the two guidelines above. One thing it’s done for me and others is to liberate us from the supposed need to eat by the clock. The benefits can be huge. In general, taking a more fluid approach seems to lead to people eating less, having more time, and being less preoccupied with food. These are usually big pluses for people.
1: Munsters MJ, at al. Effects of meal frequency on metabolic profiles and substrate partitioning in lean healthy males. PLoS One. 2012;7(6):e38632. Epub 2012 Jun 13