Intermittent fasting is the practice of eating little or nothing for some periods of time. On fasting days a person might eat nothing or no solid food or they might eat less than a quarter of the food that they normally would. Some alternate days with eating with days of fasting. Others eat normally five days a week and fast for two days. A third option is to fast for a set time every day – no food after 3pm, for example.¹

What does intermittent fasting promise to do?

Those who promote intermittent fasting promise that people who follow this eating plan will experience weight loss, loss of body fat, increased energy, lower cholesterol and decreased inflammation. There are even claims that fasting can reverse type 2 diabetes, detox the body, and make a person live longer.² Certainly, this eating plan would be a cost and time saver. Sounds too good to be true, right?

What does the evidence say?

There are very few studies on intermittent fasting in humans. Existing studies all define intermittent fasting differently, which makes drawing conclusions from them difficult. Some evidence suggests that fasting results in lower blood glucose and better insulin sensitivity, but others show no benefit.³ No data exists to support claims of detoxing or extending years of life. What about the weight loss claims? Many alternate-day fasting and whole-day fasting studies show weight loss of 3-9% body weight.¹ But without long term studies, we do not know whether this weight loss is sustainable. We do know that fasting does not lead to more weight loss than simply eating fewer calories every day.⁴

Can fasting be dangerous?

Eating too few calories in a day can increase a person’s risk of nutrient deficiency and can cause a life threatening electrolyte imbalance. Also, eating too few calories for an extended period of time can cause complications when a person begins eating again. For people with diabetes or prediabetes, not eating enough calories increases the risk of hypoglycemia. Untreated hypoglycemia can lead to seizures, coma and death.

Have a question about intermittent fasting or weight loss?

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