The survival and reproductive success of all organisms depend upon their ability to obtain food. Accordingly, animals have evolved behavioral and physiological adaptations that enable them to survive periods of food scarcity or absence. When food is not available for extended periods some organisms become dormant; for example, yeast enters a stationary phase, nematodes enter the dauer state, and ground squirrels and some bears hibernate.
Intermittent fasting is currently one of the world’s most popular health and fitness trends. People are using it to lose weight, improve their health and simplify their lifestyles. Many studies have shown that it can have powerful effects on your body and brain and may even help you live longer.
What is Intermittent Fasting?
Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It doesn’t specify which foods you should eat but rather when you should eat them. Common intermittent fasting methods involve daily 16-hour fasts or fasting for 24 hours, twice per week.
Fasting has been a practice throughout human evolution. Ancient hunter-gatherers didn’t have supermarkets, refrigerators, or food available year-round. Sometimes they couldn’t find anything to eat. As a result, humans evolved to be able to function without food for extended periods.
Intermittent Fasting Methods
There are several methods of doing IF. The most popular methods are:
- The 16/18 method. Also called Leangains protocol, it involves skipping breakfast and restricting your daily eating period to 8 hours, such as 1-9 pm. Then you fast for 16 hours in between.
- Eat-Stop-Eat. This involves fasting for 24 hours, once or twice a week, for example by not eating from dinner one day until dinner the next day.
- The 5:2 diet. With this method, you consume only 500-600 calories on 2 non-consecutive days of the week but eat normally the other 5 days.
By reducing your calorie intake, all of these methods should cause weight loss as long as you don’t compensate by eating much more during the eating periods.
IF and Weight Loss
The majority of studies of IF in humans have considered whether IF can be a potential strategy to reduce weight and correct adverse metabolic parameters amongst obese and overweight subjects.
Johnson et al. undertook the first trial of IF for weight loss amongst 10 obese subjects with asthma which tested alternate days of an 85% energy-restricted low carbohydrate diet regimen. This study reported beneficial reductions in serum cholesterol and triglycerides, markers of oxidative stress and inflammation.
The most studied IF regimen has been alternate days of 70% caloric restriction (CR), a modified form of alternate day fasting (ADF).
Most studies of ADF summarized in recent reviews show benefits in terms of reductions in weight (−3 to −7%), body fat (3 −5.5 kg), total serum cholesterol(−10 to −21%), and triglycerides (−14 to −42).
IF and Cardiovascular Disease
A study by Varady et al. performed several different studies to evaluate the effects of modified ADF on cardiovascular risk factors in overweight and obese subjects.
In one study, ADF for 2 months resulted in decreases in resting heart rate and circulating levels of glucose, insulin, and homocysteine, all of which are favorable with regards to the risk of cardiovascular disease.
In another study, 2 months of ADF reduced fat mass, total cholesterol, LDL cholesterol, and triglyceride concentrations.
A study published in the journal Circulation in 2019 by Benjamin D Horne and colleagues studied the effects of IF in patients that underwent cardiac catheterization between 2013 and 2015 and found that routine IF followed during two-thirds of lifespan was associated with greater longevity, measured as greater survival rate after the cardiac cath.
IF, Inflammation and Aging
Numerous physiological indicators of health are improved in laboratory rats and mice maintained on IF diets including alternate-day fasting and time-restricted feeding.
Among such responses to IF are reduced levels of insulin and leptin which parallel increases insulin and leptin sensitivity, reduced body fat, reduced resting heart rate and blood pressure, increased resistance of the brain and heart to stress, and resistance to diabetes.
IF can delay the onset and slow the progression of neuronal dysfunction and degeneration in animal models of Alzheimer’s, Parkinson’s, and Huntington’s diseases.
Emerging findings are revealing cellular and molecular mechanisms by which IF increases the resistance of cells, tissues, and organs to stress and common diseases associated with aging and sedentary, overindulgent lifestyles.
Although many studies have shown promising results, keep in mind that the majority of them are small studies with small groups of individuals and some of them have only been proved in animal models. Larger studies are needed to answer many unanswered questions.
Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6):1234. Published 2019 May 30. doi:10.3390/nu11061234.
Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017;39:46-58. doi:10.1016/j.arr.2016.10.005.
Benjamin D Horne, et al. Abstract 11123: Intermittent Fasting Lifestyle and Human Longevity in Cardiac Catheterization Populations. Circulation. 2019.
Kris Gunnars (2020, Apr 20). Intermittent Fasting 101- The Ultimate Beginner’s Guide. Healthline. Retrieved from: https://www.healthline.com/nutrition/intermittent-fasting-guide