The Skinny on Intermittent Fasting: How the “When of Eating” Can Impact Your Weight
It turns out that not only what and how much you eat but when you eat can impact your overall health and weight. Photo: Carol Yepes/Getty Images
“You are what you eat” is the old adage that pretty much every health expert hammers into your head at a young age.
However, over the past several years, that mantra has begun to shift a bit. Of course, quality and quantity of food — meaning what and how much you eat — are still very important dietary factors, but some experts say that “when you eat” could be just as crucial. In fact, some people even hail intermittent fasting (IF), the “when you eat”, as the secret to sustained weight loss.
Fasting is nothing new — in fact, the concept dates back to ancient times — but with the rise of the ketogenic diet, intermittent fasting has soared in popularity in recent years. A ketogenic diet (or keto diet) is a very low carbohydrate, moderate protein, high fat diet that is effective for weight loss. The keto diet involves drastically reducing carbohydrate intake (less than 50 grams a day) so that the body runs out of blood sugar as a fuel source. This reduction in carbs puts the body into a metabolic state called ketosis. In ketosis, the body becomes incredibly efficient at burning stored fat as the new fuel source. The result is weight loss.
Intermittent Fasting Is the New Ketogenic Diet
Intermittent fasting, on the other hand, encompasses a few approaches to food: eating during only certain hours of the day, refraining completely on certain days, or drastically reducing calories on a few days of the week. The idea is that abstaining from food for longer-than-normal periods of time puts the body into ketosis and, similarly to the keto diet, forces the body to burn stored fat for energy.
While some health experts insist IF is a diet, it is more of an eating pattern than a diet. The appeal of IF over the keto diet, or any other diet for that matter, is arguably that it is not a diet. If eating is limited to certain hours of the day, the reasoning goes, there’s no need to restrict calories or track carbohydrates and/or fat to experience weight loss success.
But can it be that simple?
You Are “What, How Much, and When” You Eat
It turns out that not only what and how much you eat but when you eat can impact your overall health and weight. Irregular eating times have been shown to contribute to a myriad of health problems because people don’t give their bodies a long enough break in between their feedings.
With the American diet and lifestyle of late-night takeout and Netflix, people are eating into the wee hours when historically they would have been asleep. This erratic eating behavior has been shown to cause weight gain, insulin resistance, liver damage, depression and anxiety, and other cardio-metabolic diseases. So, could longer breaks between feedings, known as intermittent fasting (IF), actually be the secret to weight loss?
Is Intermittent Fasting the Secret to Weight Loss?
The short answer: possibly, yes. While there is credible scientific evidence for IF as an effective tool for weight loss, it’s neither a quick nor a guaranteed fix for everyone.
Intermittent fasting is an eating pattern that cycles between periods of fasting and eating. And there’s a menu of at least three options on how to intermittently fast.
- Time-Restricted Feeding (TRF) involves limiting eating to a specific time window (i.e., 10am to 6pm) followed by an extended overnight fast.
- Alternate Day Fasting (ADF) means eating normally one day and then eating either a restricted caloric intake (roughly 500 – 600 calories) or eating nothing (fasting) the next day.
- 5:2 Intermittent Fasting involves eating very few calories (roughly 500 – 600 calories total per day) for two days of the week followed by five days of normal caloric intake.
All intermittent fasting methods are essentially based on the same idea: when you restrict the number of hours you eat per day and extend the number of hours you are fasting, your body runs out of food to use for energy and therefore, starts to burn stored fat. But the moment you eat again, your body will switch back to burning the food you ate for energy and store any excess food as fat.
But What Makes Intermittent Fasting Different From Simply Cutting Calories for Weight Loss?
- Intermittent fasting doesn’t require severe calorie restriction. Many people find weight loss success with IF even without severely restricting the number of calories they consume a day. For instance, a small study involving people with metabolic syndrome who fasted for 10 hours each day for three months weighed 8 pounds less, showed a higher reduction in waist circumference, lower body fat percentage, and improved insulin levels compared to those who ate throughout the day. Both groups ate the same number of calories each day.
- Intermittent fasting helps regulate insulin. Insulin is the storage hormone that is released by the pancreas in response to food. It helps blood sugar enter cells and it also signals the liver to store excess blood sugar to be used for energy later on. Simply put, the more insulin made, the more fat you store. During intermittent fasting, insulin levels drop; thus, regulating the amount of circulating insulin, which prompts your body to stop storing fat and start burning stored fat for energy. The result is not only weight loss but fat loss too.
- Intermittent fasting may decrease total daily calorie intake. A study published in Obesity suggests that, somewhat counter-intuitively, going longer without eating can actually decrease your appetite and lead to eating fewer calories.
- Intermittent fasting can sync with your circadian rhythm. Many of the human body’s processes are tied to the circadian rhythm. Your daily clock actually changes the body’s hormones and metabolism throughout the day. For example, food at the right time, such as the first meal to break your fast, provides fuel and energy, turns off the hunger hormone (e.g., ghrelin), and turns on the appetite-suppressing hormone (e.g. leptin). But food – even healthy food – at the wrong time, such as at night, inhibits the sleep hormone (e.g., melatonin), which would normally be released in preparation for sleep to block insulin production, the storage hormone. The result of late-night feeds is the release of insulin and food getting stored as fat. Put more simply, by eating in line with when your body is primed to use food, you basically hack your metabolism and manipulate your hormones to work in sync with your circadian rhythm.
Other diets, such as the ketogenic diet and other caloric restricted diets, may be just as effective as IF in helping people lose weight, but there are other health benefits that go beyond weight loss with IF. It is likely that the “success” of IF, compared to other diets, is increased insulin sensitivity for diabetes management, reduced symptoms of Alzheimer’s disease, a boost in mental clarity, reduced inflammation, improved markers of all-around health, reduced risk of chronic health conditions, improved overall energy levels, and increased longevity.
- With the rise of the ketogenic diet, intermittent fasting has soared in popularity in recent years.
- The ketogenic diet puts the body into a metabolic state called ketosis. In ketosis, the body becomes incredibly efficient at burning stored fat for energy and the result is weight loss.
- The idea of intermittent fasting is that abstaining from food for longer-than-normal periods of time puts the body into ketosis and, similarly to the keto diet, forces the body to burn stored fat for energy.
- Irregular eating times have been shown to contribute to a myriad of health problems, such as weight gain, insulin resistance, liver damage, depression and anxiety, and other cardio-metabolic diseases.
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