Featured article in the Winter 2018 Issue of Nutrition Close-Up; written by Krista Varady, PhD
Intermittent fasting has gained popularity over the past decade, but many people are still confused about what fasting entails. To put it simply, intermittent fasting involves a short period of not eating followed by a period of eating freely. Fasting does not equate to starvation, and with all intermittent fasting regimens, you get to eat every day.
The three most popular forms of intermittent fasting are the 5:2 diet, alternate day fasting, and the 16:8 diet. The 5:2 diet involves limiting food intake to 500 calories per day on two days per week. During the other five days, you can eat whatever you want with no limitations on types or quantities of foods. Alternate day fasting is slightly different from 5:2 in that it requires you to fast every other day. So, with alternate day fasting, you would continuously alternate between a 500-calorie fast day and a day of eating freely. The 16:8 diet, on the other hand, involves fasting a little bit every day. During 16:8, you would limit your food intake to an 8-hour window each day (for example 10am-6pm), and water fast the rest of the day.
During periods of fasting, it’s important to consume lots of protein. Consuming at least 50 grams of protein on the fast day will help keep hunger at bay and muscle mass high. Examples of high protein fast day meals include shakes with lots of Greek yogurt, fruits and veggies, or a large salad with lean meat, eggs, legumes or nuts.
Recent scientific evidence shows that intermittent fasting is an effective way of achieving a healthy body weight. In a recent year-long study, adults with obesity lost 6% of body weight (approximately 13 pounds) and maintained this weight loss with alternate day fasting.1 Studies also support the use of 5:2 and 16:8 for weight loss. Aft er 3-6 months of 5:2 or 16:8, people with obesity decreased body weight by 3-7% (8-15 pounds).2,3
Intermittent fasting can also help reduce the risk of developing heart disease and diabetes. Recent evidence shows that fasting can lower “bad” LDL cholesterol by up 15%, triglycerides by up to 25%, and raise “good” HDL cholesterol by up to 10%.4 Blood pressure also decreases by 5-10 mm Hg with various fasting regimens. Reductions in diabetes risk have also been observed during periods of fasting. For instance, intermittent fasting has been shown to lower blood glucose, insulin, and improve insulin sensitivity in people with obesity and prediabetes.4 Reduction in risk for heart disease and diabetes can be attributed to weight loss associated with intermittent fasting.
More recently, it’s been shown that intermittent fasting may help slow aging and extend lifespan. Studies conducted in mice show that fasted rodents live much longer than rodents who ate freely every day.⁵ These findings are complementary to human studies which show that fasting lowers several biomarkers for aging and cancer, which can help prolong lifespan.⁵ In a very recent study conducted at Harvard University,⁶ fasting was shown to help keep certain cell components in a “youthful” state, which may in turn improve life expectancy.
More and more scientific evidence shows that fasting is a great way to lower chronic disease risk, slow aging, and achieve a healthy body weight. Nevertheless, it’s important to note that fasting is not for everyone. People with type 1 diabetes or women who are pregnant or nursing should not try these diets. Moreover, children are not advised to try fasting as it may impede their growth.
Keep in mind that intermittent fasting is just one option for weight loss. While some people may find fasting easier to stick to than daily calorie restriction, others may not. All in all, people should choose a diet that they can easily incorporate into their lifestyle and stick to long-term.
1. Trepanowski JF, et al. Eff ect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Intern Med. 2017;177:930-938.
2. Gabel K HK, et al. Time restricted feeding (16:8) for weight loss in adults with obesity. Nutrition and Healthy Aging. 2018; In press.
3. Harvie MN, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond). 2011;35:714-727.
4. Patt erson RE, et al. Metabolic Eff ects of Intermitt ent Fasti ng. Annu Rev Nutr. 2017; 37:371-393.
5. Longo VD, et al. Fasti ng: molecular mechanisms and clinical applicati ons. Cell Metab. 2014; 19:181-192.
6. Weir HJ, et al. Dietary Restricti on and AMPK Increase Lifespan via Mitochondrial Network and Peroxisome Remodeling. Cell Metab.2017;26:884-896