Current opinion amongst diet experts regarding frequency of meals tells us that it is healthier to eat fewer small meals a day than one large meal. It is thought that this leads to more stable blood sugar and lower insulin levels – which leads to less fat gain and the subsequent metabolic consequences thereof, such as high blood pressure and inflammatory related dysfunctions. This practice of many small frequent meals throughout the day is referred to as “grazing”.
Two apparently unrelated studies were recently released however which seem to fly directly in the face of the grazing philosophy. The studies used mice and they compared the metabolic effects of a grazing type diet (referred to as ad libitum feeding in science) to a diet where the mice only were allowed to eat during a limited period of the day (referred to as time restricted feeding).
The first study was performed at the University of California, San Diego, La Jolla. In this study groups of mice were fed either a high fat diet or normal fat diet, with one group eating ad libitum (AL) and the second group practicing time restricted feeding (TR) where they could only eat during 8 hours of the day. Despite the fact that the animals ate the same amount of food, the TR group eating both the high fat and normal fat diets showed greater energy expenditure than the corresponding AL groups. The TR group eating the high fat diet seemed to be protected from the adverse effects of that sort of diet such as body fat gain, hyperinsulinemia, and liver dysfunction. They also showed improved coordination compared to the AL group on the high fat diet.
The second study was done at the Hebrew University of Jersusalem. The researchers looked at mice over 18 weeks while being fed a high fat diet. One group was fed AL while the other was fed TR (this time the restriction was for four hours during the day). There was also a third group that was fed a low fat diet AL. All groups consumed the same amount of calories. Compared to the AL low fat group the TR high fat group weighed 12 percent less, had 21 percent lower cholesterol, and had 1.4 times greater insulin sensitivity. The comparison to the AL high fat group was even more startling, with 18 percent less bodyweight, 30 percent less cholesterol, and a 3.7 times greater insulin sensitivity. In addition to this, plasma ghrelin (a hunger hormone) was 25% lower in the high fat TR group and plasma corticosterone (the mouse equivalent to the stress hormone cortisol) was 53% lower.
What does this all mean? This all has to do with circadian rhythms and the apparently important role it has in determining how animals utilize dietary energy. It’s a pretty complicated subject and has to do with things called clock genes and with all sorts of hormones related to the light/dark cycle. It’s known that mice and most lower animals are very influenced by circadian rhythms and these studies indicate that circadian rhythms and the timing of dietary intake have a pretty profound connection. However, we don’t know how this applies to humans. Yes, humans have circadian rhythms too but we probably are not influenced by them to the extent that a lot of other species are. In other words, this experiment may not work the same in humans at all. On the other hand, it might. My only concern is that most people I know would be so hungry by feeding time they will end up gorging and eating twice as much as they would if they had grazed throughout the day. Whatever the case, it would be interesting to find out.