Intermittent Fasting: A GP’s Perspective
What Is Intermittent Fasting?
Intermittent fasting (IF) is a popular weight loss approach. Indeed, it was the most popular diet of 2018 and the second most popular diet of 2019, according to the International Food Information Council Foundation.
IF involves a pattern of eating during certain hours or days and heavily restricting your calorie intake during other hours or days.
If you’re following the 16:8 pattern, you only eat during a certain 8-hour window (e.g. 11am-7pm) then fast for the remaining 16 hours of each day. You could do this on every day of the week or only on some of them.
If you’re following the 5:2 pattern, you eat a normal diet on 5 days of the week but fast on two non-consecutive days, consuming only about 25% of your usual calories on those days.
So, if you normally consume around 2,000 calories, you’re aiming for only 500 on your two fast days. Low-calorie ways to feel full include vegetables (make a soup) and small portions of lean protein like white fish, tofu or lean meat. Frying adds fat (and therefore calories) so boil or grill your protein. Drinking lots of water can also help you feel full. Black coffee or tea is OK if you can tolerate it – some people find it kick-starts their digestion and makes them hungry.
What Are the Benefits of Intermittent Fasting?
Research shows that IF supports your metabolism, triggers other important processes in your body, and is a relatively straightforward eating plan that helps many people lose weight.
For most of human history, we have eaten and been active during daylight hours and have slept at night, following a circadian rhythm.
Periods of fasting were also far more common. Food wasn’t always available. It had to be gathered or caught, then prepared and cooked. It was a laborious process, worlds away from our modern Western experience of man-sized fridges and pantries stuffed with tantalising snacks. When it got dark, you told a few campfire stories and then you went to bed because there wasn’t much else to do.
That’s what our metabolism has come to expect over many long years of human evolution: daytime food and activity with periods of fasting, either overnight or during times of scarcity. But it’s not how we live now. Many of us eat late into the evening, rarely (if ever) miss a meal, and snack when we’re bored or can’t sleep. But nighttime eating puts you at greater risk of obesity and diabetes.
Perhaps because of our history, fasting seems to trigger some beneficial functions. Researchers at the Johns Hopkins School of Medicine in the US recently reviewed many studies on IF and concluded that it had numerous benefits including:
- Improved metabolism
- Lower blood sugar
- Reduced inflammation
- Flushing out toxins
- Improved brain function.
So, the 16:8 IF pattern, where you only eat during an 8-hour daytime window, may benefit your metabolism. That’s good news if you’re overweight or prediabetic. One study found that obese men with prediabetes who followed the 16:8 IF pattern for five weeks had dramatically lower insulin levels and blood pressure, as well as much improved insulin sensitivity, even though they hadn’t lost any weight. Their appetites had also changed – they simply didn’t feel as hungry as they had before.
Another benefit of IF is that it’s relatively easy. You’re not weighing food, tracking points or trying to exclude whole food groups. You’re simply keeping an eye on the clock. When you do eat, you try to make healthy choices; when you don’t eat...you just don’t eat! That may be easier said than done at the beginning but gets easier as you get used to it.
Will Intermittent Fasting Help You Lose Weight?
This is the key question for many people. The answer seems to be ‘yes’, provided that you don’t overeat during the non-fasting times.
Researchers at the University of California reviewed 16 trials of IF in humans and found that 11 of those studies reported statistically significant weight loss. They concluded that almost any IF pattern can help you lose some weight.
That’s perhaps not surprising. IF limits the number of hours available for eating, meaning you’re likely to consume fewer calories, which results in weight loss.
But you do still need to pay attention to what you eat, not only to when you eat. The usual healthy eating advice continues to apply – eat fresh fruit and veg, oily fish, nuts and seeds, lean protein, whole grains and starchy carbohydrates. Don’t pig out on high-fat, high-sugar foods of low to no nutritional value or you’ll find that the kilos do not budge no matter how careful you are about the fasting periods.
It’s helpful to plan ahead so that, when it’s time to eat, there are good choices easily available. You want a small portion of nutritious and easy-to-digest food as your first meal after a fast so your body can ease back into eating. That could include a fruit or veggie juice, a vegetable soup, broth, unsweetened yogurt or kefir, or an egg.
For your next meal, you could try something that takes a bit more effort to digest. Maybe you’d like some fish or poultry, a raw, crunchy carrot, some whole grains or some nuts and seeds.
Should You Try Intermittent Fasting?
That’s really for you to decide. The Californian researchers concluded that IF may offer a promising approach to weight loss and improved metabolic health for people who are in otherwise good health and can tolerate periods of eating very little.
But IF isn’t suitable for everyone. We don’t recommend it for people with a history of eating disorders, those with chronic diseases or stomach ulcers, or for women who are pregnant or breastfeeding.
How Can We Help?
Our doctors offer support to many people trying to manage their weight or improve their overall wellbeing. Those are great goals and we’re keen to help you succeed.
If you have an underlying medical condition or other concerns about your health, please come and see us to discuss whether IF is suitable for you. If it is, we can help you get started. If it’s not, we can help you find other ways to improve your health and manage your weight. Please make an appointment today.