The food-intensive period of holidays is finally over, and most of us emerged from it carrying a few extra pounds. This is entirely natural, since evolution has enabled our bodies to store extra energy during the times of plenty, and then use it up during the times of dearth. What’s unnatural is not to allow these extra pounds to stick to the ribs (or other parts of our anatomy). Source So what kind of a New Year resolution should we adopt in order to drop these extra pounds? Actually, that’s the wrong way of thinking about it. Experience shows that any special effort at dieting and exercise is ultimately futile. Even if you stick to it, which is a big ‘if’, as soon as it’s over you start gaining those pounds back. The trick is to design your normal life in such a way that your weight goes back to some kind of healthy equilibrium after periods of excess. As readers of this blog know (too well!), the main thing I advocate is eliminating Neolithic foods from your diet – all cereals, all legumes, and dairy (I make exception for butter, however). Just doing this also naturally reduces the carbohydrate intake, which is generally good (but avoid extreme diets like Atkinson, which completely eliminate carbohydrates). When I went Paleo – really, post-Neo(lythic) – two and a half years ago I naturally lost 20 pounds of weight over a period of 6 months, without any effort to starve myself. Nevertheless, starving, or fasting, should probably be a part of post-Neo life style, and over the last year I started experimenting with it. Going without food for some periods of time is as natural as overeating, periodically. To me fasting is primarily interesting not as a weight control measure, but as a way of increasing my well-being and health. So today I’d like to discuss an interesting review article, Meal frequency and timing in health and disease, which was published a month ago in PNAS, the journal of the US Academy of Sciences. The authors consider three dietary regimes from the evolutionary point of view, and from the point of view of clinical studies of their effects. The first one is caloric restriction (CR) – reducing daily energetic intake by between 20 and 40 percent. This is an utterly unrealistic diet for most humans, no matter what are its health benefits. I’ve tried it, and basically it takes all my willpower simply to stick to it, leaving no energy for doing any work. So it’s a great way of making your life miserable and unproductive, even if long. I won’t waste time discussing CR any further. The second one is intermittent energy restriction (IER). One popular way of doing this is to fast two days a week (or greatly reduce the energy intake, to less than 500 calories), and eat normally, without any restrictions, during the remaining five days. I’ve heard that IER has been gaining popularity, and it is actually something that I could follow realistically. Sometimes it happens naturally – I travel somewhere, arrive late at night, all restaurants are closed, I go to bed hungry. Not a big deal since I know that tomorrow I will have a nice meal. The third diet regime is the most interesting. It’s called time-restricted feeding (TFR) and it involves limiting daily food intake to a 4-6 hour window. There are several reasons why TFR could have a beneficial effect on health. The first one has to do with how human bodies power themselves. When we are well-fed, the fuel that our cells use is glucose (a sugar). Glucose is stored in the liver (in the form of glycogen), and the liver releases it into the bloodstream as needed. The amount of glucose stored in the liver can power us for about 10-12 hours. If you don’t replenish this store with breakfast or snacks, it becomes depleted, and the body switches to an alternative energetic pathway: Source: Mattson et al. 2014. PNAS Now your fat deposits (yellow in the illustration) release fatty acids into the blood stream (red), which takes them to the liver (brown). There fatty acids are transformed into ‘ketones’, which go back into the blood stream and travel to the brain (blue). Brain cells use ketones as fuel. Ketones, actually, are a better fuel than glucose for cells with high energy demand, such as neurons. Interestingly enough, cancerous cells prefer burning glucose, and switching to ‘ketogenesis’ (operating by burning ketones) is one way to inhibit tumor growth. Ketogenesis also suppresses inflammation. Inflammation is usually bad news (unless your body is fighting off an infection), because it is the direct cause of arthritis, heart disease, and stroke. Fasting also shifts our metabolism into a ‘damage-control mode,’ which helps ‘cleansing’ cells of damaged molecules and organelles. In short, switching from burning sugars to burning fats is good for mental function, but bad for tumors, arthritis, heart disease and stroke. Unless you are fighting off a major infection, you are much better burning fat. A side effect of this is that you also shrink your ‘love handles,’ but I am really more interested in the health and well-being aspects, since I don’t plan on competing in a beauty contest any time soon. Source Clinical studies on animals and humans seem to be consistent with the beneficial effects of intermittent or timed fasting on health (but we need much more work to really nail it down). Last spring I started experimenting with TFR. First, I should say that even before that I stopped eating breakfasts, since I am not hungry in the morning. What I did was to skip lunch one day a week (usually, Monday). This means that by lunch time I would have already burned off all glycogen in my liver, and my metabolism has shifted to ketogenesis. I noticed several beneficial effects. First, my mental acuity seems enhanced, as is my ability to focus on the task at hand. Second, the usual ‘down time’ of the late afternoon disappears, and I can work at the same rate to the end of the working day. I feel hungry, but it is not unpleasant, especially since I know that I will eat a normal dinner in the evening. The whole fasting period is about 20 hours long. (The PNAS article suggests that intermittent energy restriction periods as short as 16 hours can improve health indicators, so 20 hours seems good enough). The only problem I encountered is that my stomach did not respond well to such fasting. So more recently I started actually eating something that has no energetic value (a tomato and a cucumber, or some radishes and a red pepper) to give my stomach something to occupy itself with. Actually, these foods have a negative energetic value (it takes more calories to digest them than the energy you get out of them). This approach seems to work well, and my New Year resolution is to start doing this TFR twice a week. What all this seems to suggest is that ketones are the best food for thought. But before you can shift to ketogenesis and turn yourself into a well-oiled thinking machine, you have to burn off those pesky carbohydrates, and that means fasting.