Does intermittent fasting work?
Intermittent fasting seems to be the diet trend of the moment. Proponents say it can lead to significant weight loss, decrease your blood pressure and your risk of developing diabetes or cancer. But what is intermittent fasting and does it actually work? Is it healthy?
What is intermittent fasting?
Intermittent fasting is essentially a diet that cycles between periods of fasting or severely restricted calorie intake and periods of eating normally.
The two most popular methods of intermittent fasting are the 5:2 diet and the 16:8 diet.
5:2 diet
The 5:2 diet involves eating normally for 5 days of the week and on the other 2 days severely limiting your calories. On the 2 fasting days you only eat 500-600 calories which is 25-30% of the recommended daily calorie intake for a woman. There are no hard and fast rules on what you can eat during the fasting days or how many meals or snacks a day you have, provided the total amount of calories doesn’t exceed the recommended amount.
Here are some examples of what a 500 calorie meal plan looks like:
https://www.taste.com.au/healthy/menus/52-diet-meal-plan/mfpp8s3z?page=Day%201
16:8 diet
The 16: 8 diet involves time restricted eating. While on it you only eat during an 8 hour window each day, for example 11am – 7pm and fast for the remaining 16 hours. There is no restriction on what you eat during the 8 hours.
What is the theory behind intermittent fasting?
The theory behind intermittent fasting is that if you go without food (or severely limit food intake) for a period of time, your body burns through its reservoir of sugar and starts to burn fat, thereby leading to weight loss.
Does it lead to weight loss?
A recent review of the results of 40 studies on intermittent fasting found that it did help participants lose weight and help burn fat. However, this comes with a caveat – participants who were on a normal calorie controlled diet lost just as much weight as those who were intermittent fasting. Nor was there any difference in the changes in body composition (lean body mass or fat stores) between the two groups.
This suggests that the reason intermittent fasting works is that by limiting the amount of time during which you can eat, you are likely to consume less calories. In other words there’s nothing magical about intermittent fasting itself.
The other thing to consider is whether or not intermittent fasting is sustainable in the long term. If it’s not sustainable, you are likely to put back on any weight you lose while on the diet once you go back to normal eating. A study published by the American Medical Association comparing the results of the 5:2 diet and a calorie controlled direct over a year found that the number of people who failed to complete the trial was much higher in the 5:2 group than in the calorie controlled diet group, suggesting it’s harder to stick to an intermittent fasting diet.
What about other health benefits?
Some studies have shown that adopting intermittent fasting may lead to lower blood pressure, a lower risk of heart disease, developing Type 2 diabetes and some forms of cancer. Again, this comes with some caveats. Few if any of these studies are long term and the reduction in the likelihood of developing chronic diseases may simply be attributable to weight loss. Again therefore there seems to be little difference between the benefits of intermittent fasting and eating a healthy diet.
Studies on animals have shown some evidence that intermittent fasting could lead to a longer life span. Again, however, similar results were achieved with other methods of calorie restriction. In the absence of human studies, there is also no way of knowing if restricting calories, either by adopting intermittent fasting or a normal calorie controlled diet will have any impact on human life span.
And not all the news is good. A recent study showed that participants adopting intermittent fasting over a 12 month showed much higher levels of LDL or “bad cholesterol” compared to participants on a calorie controlled diet over this time.
How do you know if it will work for you?
Whether or not intermittent fasting is a likely to work for you depends on the answers to these questions:
- Do you get tired, grumpy and have trouble focusing if you significantly limit your calorie intake or if you don’t eat soon after you wake up? If that’s the case intermittent fasting probably won’t work for you.
- Is it realistic with your lifestyle? If you work full time it’s likely all your meals on the 16:8 diet will need to be eaten during work hours. If you work away from home, is it realistic for you to bring 3 meals a day to work or purchase them nearby? Do you have a social life that includes eating dinner out? If so, the 16:8 diet may not fit your lifestyle.
- Do you find it easier to stick to a diet if the rules are really simple? If so then the 16:8 diet may work better for you than a normal calorie restricted diet.
- Do you eat healthy during the day but then find yourself snacking a lot in the evening? If so the 16:8 diet may help control the total amount of calories you consume.
- Are you likely to feel deprived if you can’t eat (or can only eat very little) during certain periods and make up for this when you can eat? If so, then intermittent fasting won’t work for you.
- Is this a diet plan you can see myself sticking to for the long term? If not, it’s unlikely to work for you.
- Have you had an eating disorder in the past? If so, steer away from intermittent fasting as it could act as a trigger.
- Do you have diabetes or low blood sugar? If so, intermittent fasting could be dangerous for you.
Other things to consider
If you do decide to adopt intermittent fasting, there are a few other things to consider. If you adopt the 5:2 diet it’s really important to make sure you don’t treat the non fasting days as “cheat days” and eat too many calories or unhealthy foods. The same goes for eating during the 8 hour eating window on the 16:8 diet.
Severly restricting your calories for 48 hours is likely to make you feel very weak and possibly even dizzy or light headed. So if you adopt the 5:2 diet make sure your 2 fasting days aren’t consecutive but are spaced out over the week.
Dehydration can also be an issue during fasting days / windows which can increase the risk of headaches and lack of energy so make sure to have plenty of water or herbal teas.
