The food we eat is broken down by enzymes in our gut and eventually ends up as molecules in our bloodstream. Carbohydrates, particularly sugars and refined grains, are quickly broken down into sugar, which our cells use for energy. If our cells don’t use it all, we store it in our fat cells as fat. But sugar can only enter our cells with insulin, a hormone made in the pancreas. Insulin brings sugar into the fat cells and keeps it there. Between meals, as long as we don’t snack, our insulin levels will go down and our fat cells can then release their stored sugar, to be used as energy. We lose weight if we let our insulin levels go down. The whole idea of intermittent fasting (IF) is to allow the insulin levels to go down far enough and for long enough that we burn off our fat.
Monique Tello–a physician at Massachusetts General Hospital–explains "we have evolved to be in sync with the day/night cycle, i.e., a circadian rhythm. Our metabolism has adapted to daytime food, nighttime sleep. Nighttime eating is well associated with a higher risk of obesity, as well as diabetes."
The University of Alabama conducted a study with a small group of obese men with prediabetes. They compared a form of intermittent fasting called “early time-restricted feeding,” where all meals were fit into an early eight-hour period of the day (7 am to 3 pm), or spread out over 12 hours (between 7 am and 7 pm). Both groups maintained their weight (did not gain or lose) but after five weeks, the eight-hours group had dramatically lower insulin levels and significantly improved insulin sensitivity, as well as significantly lower blood pressure. The eight-hours group also had significantly decreased appetite. Just changing the timing of meals, by eating earlier in the day and extending the overnight fast, significantly benefited metabolism even in people who didn’t lose a single pound.
Many people don't like fasting because they find it very uncomfortable. When the brain is deprived of food, appetite hormones in the hypothalamus are released in a flurry and can trigger overeating, but Mark Mattson, a professor of neuroscience at Johns Hopkins University, said the pain is temporary."Patients should be advised that feeling hungry and irritable is common initially and usually passes after two weeks to a month as the body and brain become accustomed to the new habit."
According to Tello, "new research is suggesting that not all IF approaches are the same, and some are actually very reasonable, effective, and sustainable, especially when combined with nutritious plant-based diet."
Circadian rhythm fasting, when combined with a healthy diet and lifestyle, can be a particularly effective approach to weight loss, especially for people at risk for diabetes. However, people with advanced diabetes or who are on medications for diabetes, people with a history of eating disorders like anorexia and bulimia, and pregnant or breastfeeding women should not attempt intermittent fasting unless under the close supervision of a physician who can monitor them.
Tello recommends 4 ways to use this information for better health:
1) Avoid sugars and refined grains. Instead, eat fruits, vegetables, beans, lentils, whole grains, lean proteins, and healthy fats (a sensible, plant-based, Mediterranean-style diet).
2) Let your body burn fat between meals. Don’t snack. Be active throughout your day. Build muscle tone.
3) Consider a simple form of intermittent fasting. Limit the hours of the day when you eat, and for best effect, make it earlier in the day (between 7 am to 3 pm, or even 10 am to 6 pm, but definitely not in the evening before bed).
4) Avoid snacking or eating at nighttime, all the time.