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Fast or Feed. What is Intermittent Fasting?

In the world of fitness and nutrition, trends come and go. We’ve seen Atkins, South Beach, Paleo etc., become the hottest trend for people trying to lose weight. These extreme diets aren’t easy to maintain though and people quickly fall off the wagon and go back to their normal eating habits and body composition.

Today, one of the more popular things you see people trying is intermittent fasting. The idea is that you give your body a long period of time without food. Since this way of eating is not restricting specific foods, or food types it may have you wondering if it will stick around longer than other nutrition fads we have seen, or if it will be easier to stick with.

So how does it work? I have seen 2 major ways to fast. First being people restrict food for 16 hours overnight and into the morning and eat between the hours of 1pm and 9pm. Second, people may only restrict food 1-2 times per week but for a full 24 hour period and eating as little as 500 calories on those restricted days. Historically we have been told to eat 3-4 meals a day or to eat regularly throughout the day 4-6 times. This is because our body uses glucose converted from food as energy.

Carbohydrates consumed are converted to glucose and used as energy. Fats are not as easily used as fuel and are therefore stored as triglycerides. Our body is most efficient at using glucose for energy because it is readily available after we eat and quickly converted into energy. When our glucose stores are depleted or we have not consumed any calories for an extended period of time(fasting) our bodies turn to the fat stores(triglycerides) for energy. These are released into the body as ketones. Ketones are then used by the body and brain as energy.

Much more research is needed to study the long term effects of increased ketone production in the human body since it can cause some unwanted side effects. More research will also help determine if this method of calorie restriction is really more beneficial than proper nutrition and exercise.

Some studies are trying to show that besides weight loss, there are other health benefits to forms of fasting. This study focused on insulin resistance, diabetes, cardiovascular disease and even life span. However, these studies are mostly on animals and we do not know for 100% that these results will translate perfectly to humans.

In this human study we see two groups of women, one put on 2 days of a 75% calorie restriction with no restriction the other 5 days and the other group had a 25% calorie restriction all 7 days. This study showed that there was not a huge difference between the two groups after 6 months time. “Both groups experienced comparable reductions in body fat, fat-free mass, hip, bust and thigh circumference and composition of weight loss. The percentage of weight lost, which was fat in the IER and CER groups, was 79 (±24) and 79 (±26)%, respectively”1

So if you are out there seeing and hearing about intermittent fasting and curious if it would work for you, please make sure you speak with your physician and get a referral to see a dietician. Please also remember that you don’t always have to embark on a crazy fitness or nutrition fad to see results. If you consistently eat whole nutritious foods (healthy proteins, fruits and vegetables!) and consistently exercise you will see great results in weight loss and increasing muscle tone and it will be much longer lasting than just a fad!


Sarah Mandeville

Fitness Manager, The GYM @ Milford

NASM-CPT, NASM-YES, LesMills Certified Instructor, TRX Suspension Instructor

Effects of Intermittent Fasting on Health, Aging, and Disease Rafael de Cabo, Ph.D.,and Mark P. Mattson, Ph.D.

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