Weight loss, diabetes reversal and deceleration of aging — these are the health benefits ascribed to intermittent fasting.
But does this hot new diet trend actually work?
Unlike other popular diets, such as paleo, macrobiotic or vegan, intermittent fasting is more about when you eat than what you eat. What qualifies as “intermittent fasting” (IF) is pretty broad. The term refers to a variety of diets that alternate between limited periods of fasting or calorie reduction and periods of unrestricted eating. However, three of the better known approaches are: the 16/8 method, the 5:2 diet and one meal a day fasting.
The idea is that IF reduces your body’s production of insulin, which is activated when you eat. This effect is supposed to cause your body to start burning through stored carbohydrates and eventually fat (when the stored carbohydrates run out). Proponents say that this result helps with weight loss, improved mental function, increased fat-burning, hormone regulation and reduction of inflammation.
The 16/8 method entails selecting an 8-hour window to limit all your caloric intake within. This approach allows you to choose time windows that work best for you. For example, if you can’t function without breakfast, you can limit your food intake to between 8 a.m. and 4 p.m. Or if you don’t mind skipping breakfast and love eating out late, you can go with a 1 p.m. and 9 p.m. window instead. The idea is to fast for a 16-hour window between the 8-hour periods of calorie consumption.
The 5:2 diet is split up into five days of regular eating mixed in with two non-consecutive days of consuming only 25% of your regular caloric intake. So if you regularly eat 2,000 calories a day, you would eat only 500 calories on Monday and Thursday while sticking to your regular diet the rest of the week.
The one meal a day [OMAD] approach is a 24-hour fast where you consume all your daily calories at one meal every day. For example: consuming all your daily calories at dinner then fasting until dinner the next day. You may try this a couple days a week, or some people choose to do it daily.
A 2017 study showed that IF “reduced body weight, trunk, and total body fat; lowered blood pressure; and decreased insulin-like growth factor 1.” Another study from the Harvard School of Public Health demonstrated that calorie restriction increased lifespans and ability to tolerate certain metabolic stresses in animals. However, this outcome does not directly relate to humans.
This review of forty studies of IF shows that the method is effective for weight loss averaging 7-11 pounds over ten weeks. Nonetheless, the studies were highly varied and potentially unreliable.
There has been evidence of IF’s effectiveness in animal tests, and there are studies demonstrating a strong correlation with its purported benefits. Nonetheless, more research is needed to be certain.
According to registered dietician Liz Weinandy at OSU Wexner, intermittent fasting is not a good diet for women who are pregnant or have certain conditions, including diabetes. In this study published in the JAMA Internal Medicine journal, alternate day fasting actually significantly increased the amount of unhealthy LDL (low-density lipoprotein) cholesterol — which is known as the “bad” cholesterol that raises your risk for heart disease — among the participants. In this piece in Runners World, registered dieticians warned that intermittent fasting can negatively affect athletes who require regular fuel.
While many people have seen the purported benefits that have catalyzed the intermittent fasting trend, it seems that it doesn’t work for everybody and may even pose potential health risks to some. Like all significant changes to your diet and health routine, it’s always best to speak with your doctor first.
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