Ashley Larsen, RDN has 10 years of nutrition and wellness experience specializing in empowering individuals to make permanent healthy lifestyle changes. Find inspiration for healthy living on her blog “Living with Nutrition“. For help with weight management, contact Ashley Larsen, RDN Nutrition Consulting.
The Science Behind Intermittent Fasting
by Ashley Larsen, RDN
Once again, our ears are perking up to a new diet promising weight loss and improved health. The newest buzz in the diet world is intermittent fasting.
You may have heard of this, it’s hard not to with its increasing popularity. This is very contrary to the thought of eating every 2-3 hours to “rev up” your metabolism. Often times the science behind these diets and the actual studied results get blurred and diluted once it hits mainstream and marketing takes over. We are going to take a look at the science and see what actual results the intermittent fasting diet is producing for health benefits, weight loss and fat burning.
The intermittent fasting diet (IF) is designed to reduce calorie intake to promote weight loss. Other calorie reduced diets will also promote weight loss and have shown the same benefit of improved health. So, why choose the intermittent fasting? Are there more benefits with fasting, or is this unnecessary torture?
Intermittent Fasting Benefits:
The most common instructions for the intermittent fasting (IF) diet is a daily 16 hour fast (16:8) or a 24 hour fast twice a week (5:2). It does not give instruction on what to eat but to resume normal eating on non-fasting days. The biological definition of fasting is the switch between burning glucose for energy to burning fatty acids and ketones. Once your body has been depleted of stored carbohydrates (glucose) it begins to use up fat and protein stores. Science is trying to discover if fasting helps our body shed pounds and become stronger against disease.
Most IF research is done on animals, which does not necessarily mimic the same response as in humans. A summary on the animal research has shown reduced cancer rates as compared to a normal calorie reduced diet. Also, the small sample of overweight human studies done on IF vs. calorie reduced diets show some improvement on insulin sensitivity which reduces risk for diabetes. As far as weight loss goes with IF, the research is not showing a difference between IF and calorie reduced diet when both diets are followed as instructed. However, research shows that when animal subjects fasted but overate on non-fasting days, they didn’t lose weight nor did they improve their health outcomes.
Fasting vs. Frequent Small Meals:
So does intermittent fasting burn more fat than frequently eating? During a fasting state, yes your body is burning fat for energy. However, say you burn 200 calories of fat while fasting but you later eat a surplus of 200 calories during the day then you will not lose weight. The extra calories you eat will be stored again as fat. People in the research studies on IF reported more feelings of hunger which may lead to overeating.If the intermittent fasting diet is followed as instructed then it should result in weight loss. However, you always want to keep in mind that any diet done for the short term puts you at risk for gaining all that weight back that you lost.
While research still hasn’t determined the perfect diet for weight loss, studies show that eating more frequently (3 meals and 2 snacks) can help maintain weight loss and keep you at a normal weight. Eating more frequently may help control hunger and prevent overeating.
If you are comfortable going many hours in a day without eating then intermittent fasting may be a good weight loss lifestyle for you. But, if you’re like me and get hangry and want to eat everything in sight after not eating for about 5 hours then IF might not be your best bet. For weight loss in either approach, you have to portion control and consume less than you burn. It really depends on what method would work best for your lifestyle.
Does Fasting Cardio Burn More Fat?
It’s no secret that diet is key to weight loss. But the type and intensity of exercise is also important. When you workout first thing in the morning and skip breakfast, your body will turn to fat stores for energy. Fasting cardio is best for those slow and steady workouts that target fat burning. With higher intensity interval training (HIIT) workouts, your body needs carbohydrates to burn and it’s important to properly fuel to get the best results. But, that doesn’t mean slow and steady is the best way to burn fat. Research tells us that our body only burns fat during the actual workout when you take it slow, rather than all day like shown in shorter high intensity workouts. You can burn more calories in a shorter amount of time with a HIIT workout.
So again, it all comes back to preference for your lifestyle. If you like to take it slow in the morning for a long low-intensity cardio workout then fasting cardio may be the right choice for you. If you don’t have much time to workout but want to burn fat, a short high intensity workout is also a great option but make sure to fuel with proper nutrition.
There is promising research showing potential health benefits and weight loss from intermittent fasting. However, more research needs to be done in longer human studies to determine the value of these results. Just remember that anytime you are attempting to lose weight, burn fat or get healthier it should be something that fits into your lifestyle for long term. Weight loss approaches should always be individualized to ensure safety and effectiveness based on the person. It is important to consult a health professional especially a registered dietitian when attempting an intermittent fasting diet or other lifestyle changes.