Keep Your Metabolism Humming With Intermittent Fasting

This short-term fasting technique may reduce your waistline, lower blood sugar and improve heart health.

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Within the pages of E.B. White’s famed novel Charlotte’s Web is advice from an old sheep who informs Templeton, a rat prone to gluttony, that he would live longer if he ate less. Switch to the real world, and it turns out that the sheep’s advice may hold water. 

No one would argue that eating less is the key to losing weight. But those in fitness circles generally take that knowledge and reduce their total intake but continue to eat at regular intervals throughout the day to keep their metabolism humming along and put the kibosh on gorge-inducing hunger pangs. Still, there are other ways to drop body fat, and one way that’s supported by a growing number of research studies involves shuttering the kitchen for prolonged periods — an eating pattern known as “intermittent fasting.”

When most people hear the word “fast,” what comes to mind is the fasting in response to political convictions or religious motivations such as Ramadan. In reality, we already partake in daily fasting. The word “breakfast” is exactly that — the time of day when you break the fast from the night before. Intermittent fasting, loosely defined as short-term periods of up to 24 hours during which you go without (or with very few) calories, simply extends the fasting time frame between noshes.

What it is not is a draconian detox regime on which you follow strict dietary rules such as guzzling nothing but green juices that are about as appetizing as cough syrup. With short-term fasting, you need only restrict your eating for a set amount of time ranging anywhere from eight to 24 hours. And the benefit is, when you do eat, you can serve up just about whatever foods you please. 

A (Muscular) Body of Research

A 2013 extensive review of the medical literature published in TheBritish Journal of Diabetes & Vascular Disease determined that participating in regular bouts of intermittent fasting can pay off with lower blood sugar and fat levels, healthier blood pressure numbers and improved body composition, all of which may help fend off coronary woes and diabetes. 

Why? Lead researcher James Brown, Ph.D., a lecturer at the School of Life and Health Sciences at Aston University in Birmingham, England, believes one of intermittent fasting’s main effects is to improve our cells’ sensitivity to insulin, which of course is a hormone that regulates blood sugar. Poor insulin sensitivity is a key component of metabolic syndrome, a group of risk factors that include a larger waistline, high blood pressure, and elevated blood triglyceride and sugar levels that raises your risk for heart disease, diabetes and other health woes. “There is also some evidence that intermittent fasting can reduce levels of intra-abdominal fat tissue, which is clearly beneficial for overall health,” Brown adds. 

Similarly, a 2012 study conducted by researchers at the Intermountain Medical Center in Utah had 30 healthy volunteers take part in a single-day water-only fast as well as a day of eating their usual ration of food. Not surprisingly, fasting resulted in a loss of bodyweight, a little more than three pounds. But the kicker is that much of the pudge stayed off two days after regular eating resumed. 

“Intermittent fasting, loosely defined as short-term periods of up to 24 hours during which you go without (or with very few) calories, simply extends the fasting time frame between noshes.”

Beyond improving blood-sugar control, bouts of fasting also appear to alter genes in a way that encourages the body to burn up more of its fat stores. So you’re essentially improving your body’s ability to use fat as an energy source, a worthy perk for people seeking out a six-pack they are proud to flaunt. This study also found that fasting resulted in a surge of human growth hormone, an anabolic hormone that may reduce any risk of muscle loss associated with fasting. 

More proof you shouldn’t be put off by the f-word: It’s apparent that periods of fasting can help quell inflammation in the body by lowering the activity of circulating pro-inflammatory compounds. Continually digesting and assimilating food may place added stress on the body, which could drive up inflammation and cell-damaging oxidative stress. It is now widely accepted among scientists that inflammation is a major player in disease progression. The National Institute of Aging believes that fasting for one or two days a week also may improve brain function, such as fending off memory loss. The mild stress that fasting imposes on brain cells may enhance their function much like your muscles benefit from the stress of heaving iron. 

Another worthy benefit of intermittent fasting is that it may help you better identify real signs of hunger and put a greater emphasis on nutrient-dense foods when you do eat on non-fasting days. Plus, it just might be the easiest so-called “diet” out there, requiring no counting of calories or restricting of certain food groups. “As borne out in published studies, intermittent fasting is beneficial and adherable long term, a form of eating that one uses over the course of a lifetime for long-lasting health benefits,” Brown says. 

Fasting Cheat Sheet

Want to find out whether you can shave inches off your waistline and keep your ticker beating strong by spending less time with a fork and knife in hand? Follow these guidelines for successful intermittent fasting. 

Pick Your Fast Time

While there are no steadfast rules when it comes to intermittent fasting, the basic format is to alternate days of “normal” caloric intake with days of pronounced calorie restriction. You can choose how long you want to go without calories — eight, 12, 16 or 24 hours — and for how many days a week. 

A popular intermittent fasting method is the 5:2 strategy, in which two days a week (not in succession) are classified as “fast” days and energy intake is restricted to no more than about 500 calories. On the five non-fasting days, you can eat your normal calorie load. Common 24-hour fasts involve lunch-to-lunch or dinner-to-dinner fast periods, which is beneficial if you have social commitments and takes advantage of sleeping, when you wouldn’t be eating anyway. “Everyone is different, so you need to experiment to find a fasting method that works for you,” advises James Brown, Ph.D. Consider scheduling fast days when your mind is going to be occupied by other chores. This way, you’ll be distracted and less likely to open the fridge out of habit.

Another way to manage the fast is to do a 16:8 fast, confining all caloric intake to eight hours a day. Limiting your eating in this way makes it very hard to overeat, meaning you can be a little more lax with your food choices than normal.

Start Slow

If it has become a habit to nosh several times a day, intermittent fasting may take some getting used to. Many people find it less daunting and more appealing to ease their way into fasting by, say, skipping breakfast once a week to extend their overnight fast until midmorning or later. Or try having an earlier dinner, say around 6 p.m., and then push your breakfast back to about 10 a.m. You can even experiment with a more manageable eight-hour fast by forgoing snacks and lunch between your first and last meals of the day. This way, you can slowly build up your tolerance for longer fasting periods. 

Don’t Overdo It

It’s called intermittent because the idea is to take a break from eating, not forgo it for very long periods, which can lead to health concerns and loss of lean body mass. A good guideline is to fast for no more than 24 hours and no more than once or twice a week. 

Drink Up

When fasting, it’s important to guzzle plenty of fluids to stay hydrated and minimize “empty stomach” sensations that could cause you to reach for the cookie jar. Water, seltzer water and unsweetened tea are great calorie-free hydration options. 

Keep Training

If your training goal is to shed fat, then exercising in the middle of a fast can create a metabolic environment that favors fat burning because carbohydrate stores become limited. On the flip side, if you’re training to reach a fitness goal such as nailing a certain squat weight or PR run time, it’s likely best to work up a vigorous sweat on a non-fast day. Regardless, common sense should prevail here: If you feel exhausted and lightheaded when exercising while fasting, it’s time to reach for some grub. Some fasters will aim to halt their fasts and workouts at the same time. So if you’re fasting from 8 a.m. to 6 p.m., for example, hit the gym at 4:30 p.m. and then have a healthy postworkout meal. 

Have Control

Compensatory gorging on nutritional dreck is no way to reward yourself for a fast well done. The best way to eat after ending a fast is to approach your diet as if you didn’t fast at all. So, in other words, post-fast meals and snacks should be flush with whole foods like vegetables, lean proteins and healthy fats, not deep-dish pizza and cheesecake. In particular, emphasize protein. A 2013 Purdue University study found that during periods of energy restriction, a diet rich in protein can help preserve muscle mass even as body-fat levels drop. 

Know Your Limits

Initially, headaches, fatigue and a cranky mood can be symptoms of fasting. While many people will move past these as their bodies become accustomed to fasting, for some, fasting is not in the cards and unwell feelings persist. If you always feel lousy on a fast, then intermittent fasting is likely not for you. Also, if you have any medical issues, be sure to talk to your health-care provider before starting a fasting program.