This Is What a Nutritionist Really Thinks of 16:8 Fasting
Silicon Valley moguls, celebrities, and social media influencers alike prescribe to the 16:8 diet, a form of intermittent fasting also known as the 8-hour diet. Proponents claim that restricting mealtimes — you eat during an 8-hour window each day and fast the rest of the time — helps with everything from weight loss to lowering the risk of chronic disease.
The problem with this popular method is that you’re not making decisions based on how full or hungry you feel, but rather on a restricted time window — a setup that can backfire in the long run if you're not careful. Here's what you need to know about 16:8 fasting before you start missing meals.
What is the 16:8 diet?
The 16:8 diet is a type of time-restricted fasting done to achieve better health or lose weight. (The 5:2 diet followed by Jimmy Kimmel, where you eat whatever you want five days a week and only consume 500 calories or less on the other two days, is also a modified form of fasting.)
On the 16:8 diet, you spend 16 hours of each day consuming nothing but unsweetened beverages like water, coffee, and tea. The remaining eight-hour window is when you eat all of your meals and snacks. Most people do this by starting a fast at night, skipping breakfast, and eating their first meal in the middle of the day. No foods are inherently off limits during that time, but some people will follow the keto diet at mealtimes to supercharge their weight loss.
While the term intermittent fasting (or IF) may be new to many of us, the practice isn’t all that different from the way our ancestors likely lived: Hunt, gather, and eat during daylight; sleep and fast during darkness.
Is 16:8 fasting good for weight loss?
Some studies have found that there’s virtually no difference between people who regularly practiced intermittent fasting and those who simply cut back their calorie intake overall.
A growing body of research demonstrates that a better strategy is optimizing the nutritional quality of what you already eat (veggies, fruit, lean protein, whole grains, and healthy fats) versus fasting or counting calories. Also, science suggests any potential benefit from fasting is quickly undone during the eating part of the cycle, in which appetite-suppressing hormones switch gears to make you feel even hungrier than you felt at baseline.
But some dieters may benefit from daily fasting if they have trouble sticking to prescribed meal plans or restrictive diets; a 2018 pilot study published in the Journal of Nutrition and Healthy Eating suggests that a 16:8 fasting plan can help obese dieters lose weight without having to count every single calorie they eat. This approach to fasting could also aid those battling other weight-related issues — namely, high blood pressure. A new scholarly review published in the New England Journal of Medicine suggests that a 16:8 fasting plan may help the body naturally improve blood sugar regulation, as well as decrease blood pressure overall in the long run.
Is fasting 16 hours a day healthy?
Forms of intermittent fasting like the 16:8 diet rely on the concept that fasting reduces oxidative stress on the body, which can decrease inflammation and the risk of chronic diseases.
It’s also theorized that fasting gives your vital organs, digestive and absorptive hormones, and metabolic functions a “break,” according to a recent study published in Cell Metabolism. Since our bodies secrete insulin to help our cells absorb sugar, fasting is linked to reducing our susceptibility to insulin resistance over time. (High insulin levels ultimately put us at risk for a whole host of diseases.)
However, research has also linked fasting to increases in LDL cholesterol (the "bad" kind). Intermittent fasting can make you feel dizzy and nauseated and cause periods of low-blood sugar and dehydration. Despite the fact that most 16:8 enthusiasts drink water during fasting periods, it may not be enough (reminder: food itself provides quite a bit of water).
I also have a much deeper concern about the disordered eating behaviors that may arise from intermittent fasting. Research shows that fasting for a period of time followed by a limited window for eating primes you to overeat. It's a cycle that can be difficult to get out of because it impairs our body's natural hunger cues and metabolism. Restricted eating may also lead to an increased risk of depression and anxiety.
This is especially concerning for women, who have historically been more likely to develop eating disorders. The allotted periods of restriction followed by eating lends itself to binge-purge tendencies that cannot (and should not) be ignored. According to the National Eating Disorders Association, periods of fasting and binging are considered risk factors for eating disorders.
Should you try 16:8 fasting?
Ultimately, it's a personal choice. But there are a few beneficial behaviors you can try without committing to the riskier elements of 16-hour fasts. The first is to better understand mindfulness and how it relates to your food choices. To get started, consider these questions when you're deciding when and what to eat:
Where are you physically when you decide to eat?
Many of us eat based on scenario, not hunger levels. Case in point: Raise your hand if you’ve ever gone to the movies after dinner and suddenly wanted popcorn? Yep, me too!
By considering the moments when you eat, you may become aware of patterns you didn't notice before. Say you’re a person who loves to graze during The Bachelor. If you’re fasting after 8 p.m., you’ve automatically cut hours — and subsequently, calories — from your post-dinner snacking.
Are you getting enough sleep?
If you've cut out late-night snacking, that alone could help you go to bed earlier — a very crucial component to any weight loss plan. Getting seven hours of sleep per night has been linked to better weight management, reduced risk of chronic disease, and improved metabolism.
The bottom line: It’s simply not feasible for many of us to restrict food entirely for set periods of time in order to achieve better health. In addition to being difficult socially (who wants to skip happy hour or dinners with friends?), self-imposed rules are simply not as joyful as having the right information and making choices that empower you versus hold you back. It's best to find ways to make eating nutritious food work for you in the context of your day-to-day life. If you are considering intermittent fasting, I’d encourage you to try it by starting small and keeping it as simple as possible: Close your kitchen after dinner, aim to get more sleep, and sit down for a full breakfast at your usual time tomorrow.
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