Jason Fung, MD, taught me how not to eat. I never realized I could skip meals and have greater mental clarity and more energy.

In his book, The Obesity Code (Greystone, 2016), Fung, a nephrologist turned obesity physician, describes with great clarity and solid science that obesity is a hormonal illness: the central hormone is insulin.

In medical school we are taught that insulin is the hormone that allows sugar to enter cells for energy. Type 1 diabetics lose their capacity for making insulin in the pancreas and will die unless they get insulin. Curiously, type 2 diabetics, currently over 90 % of those with diabetes, have excessive insulin and what is called insulin resistance, that is, the insulin does not work well in lowering blood sugar.

More importantly, as Dr. Fung points out, insulin is a fat storage hormone. When we stress our body with excess carbohydrates, insulin pours out and “locks the door” for burning fat. Any excess carbohydrates we do not burn for energy become fat through lipogenesis. The actual biochemistry is more complicated, but the general principle as stated is true. When we expose ourselves to a daily ample amount of carbohydrates, our daily high insulin level results in insulin resistance, overweight or obesity, type 2 diabetes and even high blood pressure and high cholesterol.

Our bodies did not evolve to eat carbohydrates like we do today, averaging 60% of our daily food intake in calories. Back when we ate the foods of nature – root vegetables, whole fruit, nuts, wild meat, eggs and fish – the dominant nutrient was fat followed by protein and then carbohydrates, only about 15% of calories. That is the evolutionary human diet; what we eat today with processed foods is not what our body wants. Excess insulin with its high blood sugar is a stress response that causes poor health, even dementia.

The key to reducing fat is to get your insulin level low. Fasting insulin is now regarded as an important lab test that should be part of any routine check-up. Fasting blood sugar roughly correlates; however, the fasting insulin reflects more time in the body than a spot blood sugar.

The current “normal range” for fasting insulin is silly, being 2.5 to 26, a whopping difference. Normal ranges are established from an average of what most people have in their blood. In order to lose weight, the fasting insulin should be below 10. Without that, diets and exercise are a waste of time and effort. To avoid dementia, the fasting insulin should be below 5 or 4.5 per Dr. Dale Bredesen, author of The End of Alzheimer’s (Penguin, 2017).

Any time we eat, no matter what we eat, insulin in the blood goes up. Obviously with carbs it goes up higher. Fung points out that we have been focused only on what we eat and not focused on the equally important when we eat. We did not evolve to eat three meals a day and to snack in between. More natural in the history of our species is to eat 1-2 times a day, and drink only water in between.

Fasting has been part of our history for thousands of years. Judaism, Christianity, and Islam all honor fasting, even for days at a time. All report mental clarity, inspiration and other health benefits from fasting. Fasting even just 12 or more hours in a day may lower insulin levels.

Fung is the founding director of the Intensive Dietary Management Program at the University of Toronto. There he uses fasting as a core modality and is successful in reversing obesity and type 2 diabetes. A variety of fasting programs is used, depending on the person, from part of a day to as long as three weeks. The documented record for a medically supervised fast is 382 days in a male weighing over 400 lbs. With exercise, all muscle is preserved during a fast. Besides water, minerals and electrolytes are consumed, such as in bone broth.

Our cultural eating pattern of three meals a day is more psychological than physical. We think we are hungry and need to eat, but we do not. Carbohydrates drive hunger through blood sugar fluctuations, so fasting is much easier with a low carbohydrate diet.

I have started recommending intermittent fasting to patients and many have lost weight where they failed on just a low carb diet. I do this myself, eliminating snacks and skipping lunch. The method of eating two meals a day in one eight-hour period, for example from 11 AM to 7 PM gives 16 hours of fasting daily and is very effective in lowering insulin levels and fasting sugar, as well as burning fat. Staying hydrated with water is vitally important during a fast and helps to suppress hunger; morning coffee, even with a little butter or cream (but no sugar), will not break a fast as the effect on insulin levels is minimal.

Thanks to Jason Fung, MD, and others we have a much clearer physiologic understanding of overweight, obesity and type 2 diabetes. Fasting is a powerful tool to add to any diet program for better health.

Dr. Scherger is Vice President of Primary Care at Eisenhower Medical Center. He is also the Marie E. Pinizzotto, MD, Chair of Academic Affairs, and Clinical Professor of Family Medicine at the University of Southern California Keck School of Medicine.