Diet Review - Intermittent Fasting

From bookstores to social media to blogs, there’s no shortage of information on diets for weight loss and for better health. So how to differentiate what “works” from an overhyped fad?

It’s important to remember that even if a particular diet may be successful for one person, it may not be effective for another due to individual differences in genes and lifestyle. Research shows that calories matter, but focusing on food quality is an equally important part of preventing weight gain, promoting weight loss and stave off chronic diseases. Diets are also more likely to be successful when they are easier to follow, so tailoring a strategy to suit your own lifestyle is key.

Still, when faced with the seemingly endless promotion of weight-loss strategies and diet plans, it helps to see what evidence is supporting them. In this first article, I take a look at intermittant fasting. In the articles to come I will review other popular diets.

Intermittent Fasting

Intermittent fasting is a diet regimen that cycles between brief periods of fasting, with either no food or significant calorie reduction, and periods of unrestricted eating. It is promoted to change body composition through loss of fat mass and weight, and to improve markers of health that are associated with disease such as blood pressure and cholesterol levels. Its roots derive from traditional fasting, a universal ritual used for health or spiritual benefit as described in early texts by Socrates, Plato, and religious groups. Fasting typically entails a steady abstinence of food and beverages, ranging from 12 hours to one month. It may require complete abstinence, or allow a reduced amount of food and beverages.

Prolonged very low calorie diets can cause physiological changes that may cause the body to adapt to the calorie restriction and therefore prevent further weight loss. Intermittent fasting attempts to address this problem by cycling between a low calorie level for a brief time followed by normal eating, which may prevent these adaptations. However, research does not consistently show that intermittent fasting is superior to continuous low calorie diets for weight loss efficiency.

How It Works

The most common methods are fasting on alternate days, for whole days with a specific frequency per week, or during a set time frame. 

  • Alternate-day fasting—Alternating between days of no food restriction with days that consist of one meal that provides about 25% of daily calorie needs. Example: Mon-Wed-Fri consists of fasting, while alternate days have no food restrictions.

  • Whole-day fasting—1-2 days per week of complete fasting or up to 25% of daily calorie needs, with no food restriction on the other days. Example: The 5:2 diet approach advocates no food restriction five days of the week, cycled with a 400-500 calorie diet the other two days of the week.

  • Time-restricted feeding—Following a meal plan each day with a designated time frame for fasting. Example: Meals are eaten from 8am-6pm, with fasting during the remaining hours of the day.

The Research So Far

Physiologically, calorie restriction has been shown in animals to increase lifespan and improve tolerance to various metabolic stresses in the body. The evidence for caloric restriction in animal studies is strong. In humans, however, this has not been firmly established, and for fairly obvious reasons - a randomized clinical trial measuring the lifespan in people who fast versus those who do not fast would be impossible to do. Nevertheless, proponents of the diet suggest that the stress of intermittent fasting causes an immune response that repairs cells and produces positive metabolic changes (reduction in triglycerides, LDL cholesterol, blood pressure, weight, fat mass, blood glucose).  An understandable concern of this diet is that followers will overeat on non-fasting days to compensate for calories lost during fasting. However, studies have shown this not to be true when compared with other weight loss methods. 

Results of one of the best studies we have of intermittent fasting in humans showed that fasting every other day for 12 weeks caused 32 people to lose an average of 12 pounds more than those who followed a daily program of calorie restriction. The intermittent-fasting group also demonstrated marked lowering of several heart attack risk factors:
• They lost an average of eight pounds of fat.
• Their triglycerides dropped 20 mg/dL. 
• Their bad LDL particle size increased. A desirable affect, as the larger the particle size, the less likely you are to become diabetic.
• CRP (a measure of inflammation and heart attack risk) decreased 13 percent.
• Blood adiponectin increased six percent, also a measure of reduced risk of developing diabetes.
• Blood leptin decreased 40 percent. Lowered leptin levels indicate fat loss.

In another study, 107 overweight women who spent six months eating 650 calories per day for two days a week lost an average 14 pounds of fat and 3 inches from their waists, compared to 11 pounds of fat and 2 inches from waist for daily calorie-restricted dieters (Int J Obes, 2011 May;35(5):714-27).

Intermittent Fasting May Help Prevent Disease

A review of the medical literature shows that intermittent fasting can lower blood sugar and fat levels, reduce high blood pressure, help people lose weight, and help to prevent and treat diabetes and heart attacks. Intermittent fasting lowered blood pressure, resting heart rate, cholesterol, triglycerides, weight, and blood sugar levels, according to a study reported at the Annual Scientific Sessions of the American College of Cardiology in New Orleans (April 3, 2011). Another study showed that intermittent fasting caused a greater change in:
• body weight,
• fat mass,
• signs of diabetes (belly fat, blood sugar and insulin levels, and LDL particle size), and
• heart attack risk factors (LDL cholesterol, homocysteine, and heart rate (Nutrition Journal, 2012;11:98).

Intermittent Fasting May Prolong Life

A high rise in blood sugar, and subsequently in insulin, after meals damages every cell in your body and increases risk for diabetes, heart attacks and many cancers. Intermittent fasting appears to help you lose weight by making your cells more sensitive to insulin. Fat inside cells blocks insulin receptors and prevents insulin from doing its job of lowering high blood sugar levels. One study shows that mice that eat fatty foods for eight hours a day and then are forced to fast for the next 16 hours of each day do not gain weight or lose their ability to respond to insulin.

The meal-skipping mice gorge when provided food so they do not eat fewer calories than mice on unrestricted diets. Mice that fast every other day while eating double the normal amount of food on non-fasting days have better protection from becoming diabetic (lower insulin and sugar levels and better response to insulin), and less brain damage than mice on 40 percent calorie-restricted diets (Proceedings of the National Academy of Sciences, May 13, 2003; 100(10):6216-6220; and The Journal of Nutrition, June 2003;133 (6): 1921-1929).

Try Intermittent Fasting Yourself

Future studies will tell if intermittent fasting is more effective than overall calorie restriction in preventing disease and prolonging lives in humans. Meanwhile, you may want to try intermittent fasting to lose weight or to avoid the weight gain that often comes with aging.

Try the 5:2 approach. Eat your normal diet five days a week. Pick any two days of the week to restrict your intake of food to fewer than 700 calories. You will get the best results if your "normal diet" is a healthy one, but you do not need to try to restrict calories on your non-fast days. You should eat plenty of vegetables, fruits,whole grains, beans, seeds and nuts. You can include moderate amounts of fish and chicken. I recommend that you restrict red meat, processed meats, fried foods, all drinks with sugar in them, and sugar-added foods and desserts. Adding exercise to your program of intermittent fasting will help you to lose even more weight.