Friend or Fad: Are These Trendy Diets Good for You?
Registered dietitian Lisa Muras weighs in on the pros and cons of five popular food regimens.
What is it?
Fasting is generally defined as abstinence from all or certain foods and/or beverages for a specified period of time. It has been practiced for centuries, often as part of religious practice. When used as a weight loss method, fasting can take many forms: alternate day fasting (fasting for 24 hours, then eating normally for the next 24 hours); modified fasting such as the 5:2 diet (eat normally but healthfully for five days of the week and consume a very low-calorie diet of 500 to 600 calories on two nonconsecutive days); or time-restricted fasting (eating only during a specific time frame, such as 10 a.m. to 6 p.m.).
A large body of research exists on laboratory animals showing that some types of fasting can reduce the risk of diseases such as diabetes, cardiovascular disease, Parkinson’s disease and stroke. Some small studies on humans have shown significant short-term weight loss, decreases in body fat and a reduction in triglycerides, LDL cholesterol and systolic blood pressure. It is believed that fasting may lead to improved health because it positively influences circadian rhythms (thus improving sleep), and helps activate adaptive stress responses to protect against disease. Traditional daily caloric restriction can slow your metabolism rate, but eating normally most days of the week with fasting two or three days may actually accelerate metabolism.
Most meaningful research has been conducted on animals, so the results of a fasting diet on human subjects is unclear. Also, the term “fasting” is widely interpreted, so it is difficult to compare results. While some research indicates intermittent fasting can be effective for short-term weight loss, it doesn’t appear to be effective in keeping the weight off over time. Adherents to this diet may find it difficult not to overeat or “cheat” on non-fasting days, which can thwart weight loss. Also, many following a fasting “window” tend to skip breakfast, which has been shown to increase the risk of cardiovascular disease while decreasing cognitive function and energy. On fasting days, many individuals report feelings of lethargy, headaches and low blood glucose, although this can improve over time. A well-rounded eating pattern provides both calories (energy) and micronutrients, such as vitamins and minerals, that would be missing when fasting and difficult for most people to meet in one day.
Going longer between meals and snacks may be beneficial, particularly if you struggle with late-night snacking. The constant “grazing” that typifies a Western diet complicates metabolism, adds excess calories and can even disrupt sleep. Fasting in the evening and overnight, then eating regular meals during the day, is the pattern that appears to have the most benefits in terms of weight loss, blood sugar control and improved lipids. It’s also the most tolerable.