Intermittent fasting has quickly become one of the hottest topics in the weight loss community. Research on intermittent fasting has produced promising short-term results, but more long-term human studies are needed to understand the potential health benefits and risks. Nevertheless, many people are jumping on this weight loss bandwagon. But, before you do, here’s what you should know about various intermittent fasting regimens so you can make an informed choice.
Types of Intermittent Fasting Regimens
Alternate day fasting (ADF) requires you to alternate fasting days (consuming 0-25% of energy needs) with unrestricted eating days. In the majority of ADF studies, participants consumed 100-125% of their energy needs on eating days and did not eat excessively.
The 5:2 Diet is a type of periodic fasting in which you eat as usual on five days of each week, and fast (consuming 0-25% of energy needs) on two days of each week.
Time-restricted feeding (TRF) requires fasting overnight for 12 to 16 hours and restricting your daily feeding window to 8 to 12 hours. A common daily TRF schedule involves fasting overnight for 16 hours, skipping breakfast and eating only during an 8-hour window such as 11:00 AM to 7:00 PM.
All types of intermittent fasting allow you to eat as desired during the feeding window. There are no specific recommendations for calories or macronutrient ratios. But for optimal health (and weight loss) you should eat nutrient-dense, whole foods and avoid junk food loaded with sugar, fat and sodium.
Fasting Mimicking Diet
Dr. Valter Longo at the University of Southern California developed the fasting mimicking diet based on his research on longevity and cell metabolism. The FMD is a type of periodic fasting using a patented high-fat, low-calorie, plant-based diet called ProLon for five days each month for three months.
Outcomes of this diet include reductions in weight, visceral fat, blood glucose, blood pressure, cholesterol levels, inflammatory markers, and IGF-1, which is linked to cancer cell growth. This diet may also enhance stem cell-based regeneration and removal of aging and damaged cells to increase longevity.
Because of the risk of hypoglycemia when following this diet while taking medications that reduce blood glucose, this diet is not recommended for people with diabetes. Medical supervision is recommended for people diagnosed with certain health conditions. Read more about the contraindications for the ProLon diet here.
Health benefits of fasting:
After an individual has fasted for at least 12 hours and glycogen stores are depleted, the pancreas stops secreting insulin in response to increased blood glucose levels after a meal. High levels of insulin prevent the breakdown of fat cells for energy and promote fat storage. Also, cells hold three grams of water for every gram of stored glycogen, so depleting glycogen stores also releases water weight. During fasting, the body switches from using glucose for energy to releasing stored fat and producing ketones for fuel.
Many studies of intermittent fasting in both animals and humans have found improvements in heart disease and diabetes risk factors such as insulin resistance, cholesterol levels, inflammation, visceral fat mass, and weight loss equal to that achieved by calorie restriction diets.
But a 2017 review on the metabolic effects of intermittent fasting published in the Annual Review of Nutrition, found limited data on the long-term clinical outcomes for diabetes, cardiovascular disease, Alzheimer’s and cancer.
Risks of fasting and who it’s NOT for:
A Brazilian study of rats who fasted on alternate days for 3 months found pancreatic insulin-producing beta cell damage with increased markers of insulin resistance and oxidative stress. Even though the rats lost weight and ate less food, their abdominal fat levels increased.
The American Heart Association recently published a scientific statement on meal timing and frequency based on the existing literature, including three large, long-term prospective studies that found that skipping breakfast increases the risk of developing type 2 diabetes. The authors concluded that irregular eating patterns may not benefit metabolic and heart health, and that although intermittent fasting may produce weight loss, there’s insufficient data to show that the weight loss can be maintained in the long term.
Fasting diets are not recommended for anyone diagnosed with hypoglycemia, eating disorders or disordered eating patterns. Pregnant women and individuals who take medications for health conditions such as diabetes and thyroid disease should not fast. Consult your personal physician before changing your diet or fasting regularly to prevent medical problems.
Summary of Intermittent Fasting:
In November 2018, The American Journal of Clinical Nutrition published the results of the largest randomized clinical trial of intermittent fasting to date. In this study, 150 overweight and obese humans were assigned to a diet of intermittent fasting (5:2), a calorie-restricted diet or a control group, where both diets resulted in a weekly calorie deficit of 20%. After 12 weeks of dieting and 12 weeks of maintenance, plus 26 weeks of follow up, researchers found that intermittent fasting and calorie restriction were equally effective, producing a loss of 5.2% and 4.9% of body weight, respectively, after 50 weeks. Long-term changes in visceral and subcutaneous fat tissue were proportional to weight loss, and there were no significant differences in biomarkers of metabolism.
In many animal studies and a limited number of human studies, intermittent fasting appears to promote weight loss, but more large, long-term randomized trials are needed to determine the safety and efficacy of fasting, as well as the optimal fasting interval and energy requirements for fasting and non-fasting days to make specific dietary recommendations.
A saner approach to Intermittent Fasting:
To achieve permanent weight loss and optimal health, you should choose a healthy and sustainable eating style that fits your lifestyle. If you want to experience some of the health benefits of fasting, try this conservative approach to TRF: eat three nutritious meals daily during a 12-hour feeding window (e.g. eat from 7:00 AM to 7:00 PM), and stop eating late at night so you can fast for 12 hours overnight, which may be long enough to make the metabolic switch from using glucose to breaking down fat for energy.
Combine this strategy with an intuitive eating approach that allows your internal signals of hunger and fullness to determine when and how much you eat. This is a great way to meet your nutrient needs without overeating calorie-dense foods, especially at night, which has been linked to obesity.