If weight loss was easy nearly two out of every three American adults probably wouldn’t be overweight or obese. Clearly, weight loss is a challenge for many. Intermittent fasting has been getting a lot of attention as an approach to losing weight and achieving health. For some people, it works because it’s simpler than counting calories. So what exactly is intermittent fasting?
Although many people choose intermittent fasting as an approach to losing weight, it isn’t really a diet — it’s a specific pattern of alternating eating and fasting. There are no restrictions on what you can eat (but a healthy diet is always recommended); it’s all about when you eat, and when you don’t. There are a number of approaches to intermittent fasting.
People take up intermittent fasting for a number of reasons. Fasting has been around for centuries, often tied to religious practices. Research has shown it may improve some neurological conditions, can enhance cognitive functioning, increases resistance to stress, improves immunity and helps delay the effects of aging(1,2,3).
From a weight loss perspective, fasting’s appeal comes from the fact that once your body uses up all the available energy from the food you’ve eaten, called glycogen, it starts burning your fat for fuel. As long as you maintain a reasonable diet on your non-fasting days, intermittent fasting can be an effective way to lose weight.
Fasting is an individual experience for everyone, and no one type works best. For some people, pregnant or nursing mothers and people with eating problems, it’s better avoided. Before starting a fast, it’s a good idea to talk to your doctor, especially if you have an underlying health condition, such as diabetes or kidney stones.
In a word, yes. Working out while fasting is possible and some people even prefer working out in a fasted state because theoretically you are burning body fat for fuel. If you do choose to fast and work out, there are some things to keep in mind to get the most out of both the fast and the exercise. The type of fast you are doing may influence what kind of exercise you can tolerate. Because time-restricted fasting is close to a normal eating pattern, you may be able to continue with little change to your normal workout routine. If you’re doing a more extreme fast, like alternate day, you may want to limit your activity to something less strenuous such as brisk walking or a gentle form of yoga. There may be some trial and error involved until you figure out what works best for your individual needs and goals(1,2).
The timing of your workouts when fasting can be one of the most important things to consider. You’ll want to factor in the type of exercise, what kind of fast you are on and personal preference. Many people do fasted cardio, opting to go for a run first thing in the morning, for example.
If you’re doing time-restricted fasting, working out in the morning will tap into your fat stores for fuel, because by then your glycogen stores — the energy from the food you eat — will be nearly gone. For optimal results from the exercise itself, eat a meal that includes about 20 grams of protein no more than 30 minutes after the exercise, or you’ll risk breaking down your muscles for fuel instead.
A lot of people can’t or don’t want to work out on an empty stomach. If that’s you, you have some options for times to schedule workouts within your eating “window.” If the workout you’re planning is very intense — for example leg day — you may want to schedule it relatively soon after a meal, and make sure you’ve eaten some high-quality carbohydrates.
There are side effects to consider when working out in a fasted state. You’re likely to be weaker and have less stamina. This is normal and you should avoid pushing yourself too hard if you don’t feel up to it. If you have a tendency to “bonk” — the physical response when all the glycogen in your liver and muscles is depleted(4) — you may experience moodiness while fasting and possibly headaches or nausea. You may also find it hard to focus. However if you stick with it, most side effects usually subside within about a month(2).
To help your mind and body adjust through the first month and beyond, there are some supportive practices you can undertake.
There are safe and effective ways that you can work out while doing intermittent fasting. Be clear about your goals before you start. Talk to your doctor or dietitian before starting to make sure you’re a good candidate for fasting. Don’t be afraid to have a bit of trial and error to figure out how your body reacts to different schedules. Be prepared to time your workouts and modify their intensity depending on where you are in your fasting cycle, and set yourself up for success by listening to and supporting your body during the process.
Laura High - Contributing Writer, Physician's Choice