Intermittent fasting is a way of eating in which one fasts for a period of time each day. Often one eats the same amount of calories one is used to, but only during a seven-hour period; water and tea can be ingested throughout the day. In a typical regime, a person eats the first meal of the day in the early afternoon, followed by a snack in the afternoon and dinner in the early evening; nothing more is eaten until the following early afternoon meal. This enables at least 16 hours during which no calories are consumed.
The goal is to change one’s metabolism from glycosis, in which sugar is used as a fuel source, to ketosis, the metabolic state in which energy primarily comes from ketone bodies, or fats. With this method, we can slowly shift from being sugar-burning to fat-burning animals.
Our bodies normally run on glucose. The food we eat is broken down into sugars, and insulin is produced to bring the sugars into the cells and mitochondria where energy is made. When the glucose from our meal runs out, we produce cortisol, whose job it is to take the stored glucose out of storage. We have about 24 hours of glucose available before we start breaking down fats.
There are many reported benefits of burning fats rather than sugars. First, when we burn fat as a source of energy, we lose fat that is stored in our bodies, enabling weight loss. Triglyceride levels decrease, lowering heart disease. Inflammation is lowered, which in turn lowers the symptoms of inflammatory illnesses. Insulin and leptin sensitivity is increased, helping stabilize blood sugar and combat chronic disease. Energy increases, because fat provides a far more efficient method of energy delivery than does sugar. Ghrelin levels are increased, helping manage hunger. The digestive tract gets a chance to rest, which can be helpful for many digestive issues. The list goes on. Regulate blood sugar and hunger, have more energy, lose weight, decrease the chance of cancer, diabetes, heart disease—what more could you want?
Paleo diets are often recommended with intermittent fasting, along with the more extreme ketogenic diet, a fat-based diet developed by the Johns Hopkins Medical Center for treatment of epilepsy. My minimum suggestion is to eat real food (as opposed to processed food), complex carbohydrates in small portions only, plenty of vegetables and good-quality meats and fats. Sugars and any foods that cause inflammation for you are out; common symptoms of inflammation are bloating, sinus congestion and headaches.
It is also recommended to exercise right before eating the first meal of the day. Being in the ketogenic state while exercising—especially high-intensity exercise—can increase human growth hormones and counteract muscle aging and wasting.
Not everyone should try this diet, however. If you are pregnant or have blood sugar or chronic health issues it is important to check with your doctor first, and be closely monitored if you do try it. For others, the idea of not eating sugar or wheat represents a major change; many people have deep attachments to these foods, and their identities are wrapped up in them. These things need time to sort out. On the other hand, I have seen profound results from people who do try this approach to eating.
It is thought that the reason intermittent fasting can make such a difference is that we were designed to eat this way. Throughout our evolution, we have spent long periods of time fasting, as opposed to the constant grazing and over-eating so common today. Some have described the approach as finding a deep and sturdy old friend who has been buried under the indignancies of modern indulgence.
Jonathan Gavzer is a licensed acupuncturist, manual therapist, practitioner of Functional Medicine and West Marin resident.