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The Lowdown on Intermittent Fasting - Brianna Bavota R.D.

Nov 10, 2020

There is nothing new about fasting. In fact, it is one of the oldest dietary interventions and has been part of the practice of every culture and religion.  

Since 2010 the number of online searches for “intermittent fasting” has increased by over 10,000%, as people recognize the significant health benefits, including weight loss, improvements in insulin resistance, type 2 diabetes, blood pressure. There may be benefits in reducing oxidative stress and inflammation in the body, both of which can lead to heart disease. There is still some mixed data on whether intermittent fasting outperforms other methods of calorie restriction for weight loss, but a really nice added benefit of fasting is that studies have found that it leads to decreased appetite - so you’re not hungry all the time – and wouldn’t that make losing weight a whole lot easier?


Intermittent fasting is a controlled, voluntary abstinence of food. It is where you eat all of your day’s food within a specified time window. Food is available, you simply choose not to eat it. The non-eating period is called “fasting”. Everyone fasts daily to a certain extent, for varying lengths of time. For example, everyone fasts overnight, while they are sleeping, with “breakfast”, the first meal of the day, ending the fast. In fact, our bodies are designed to fast, to store food in times of availability, and in times of scarcity, to release it – it comes naturally to us! 


Having longer periods of time with no food intake allows lowering of your body’s insulin levels. A great percentage of people in North America have hyperinsulinemia leading to weight gain and the pickle of the situation is that obesity also drives high insulin levels, or insulin resistance. It’s a vicious cycle. But not eating, means that you aren’t stimulating insulin production by your pancreas, and therefore serum insulin levels can drop – this allows your body to tap into your stored energy (i.e. fat) as a fuel source.

The second benefit of intermittent fasting is lower calorie intake because food is limited to certain time windows. In fact, studies looking at closing the eating window to 4, 6, or 8 hours of the day have found anywhere from calorie reduction of 350 to 550 calories in a day.

So, lowering insulin and reducing overall calorie intake are two ways intermittent fasting may help with weight loss.


-       Fasting actually REDUCED hunger – which is pretty great!

-       INCREASED ENERGY, this is thought to be due to an increase in adrenaline during fasting periods

-       It’s SIMPLE, there is less opportunity for your reward brain to derail you from your healthy choices, so less brain chatter.

-       It’s FREE, and saves time in meal prep.

-       There is no special equipment, foods, or supplements along with it.

-       And it provides FLEXIBILITY, in the sense there is no perfect way to fast


Now there are a variety of ways from hours, days and weeks. Shorter fasts are generally done more frequently. Longer fasts are typically twenty-four to thirty-six hours, done two to three times per week. The three most common forms of fasting studied in the literature are:

-       Time-restricted eating 16:8

-       Alternate day fasting

-       Or 5:2 fasting

The most popular fasting period is 16 hrs. This is also called Time Restricted Eating, because you’re restricting food intake to a smaller window during the day. This regimen involves using a daily 16-hour period of fasting and an 8-hour ‘eating window’. For example, this would mean eating from 11 am – 7 pm, and fasting from 7 pm to 11 am. This generally means skipping the morning meal every day. Some people choose to eat 2 meals during that 8-hour window and others will eat 3. It’s really important that the timing of fasting coincides with your circadian rhythm – that is, you don’t want to fast all day and eat all night, because that typically leads to weight gain because of the hormonal effects. In fact, some people call 16:8 fasting, “circadian rhythm fasting”.

There is also 20 hr fasting. This involves a 4-hour eating window and a 20-hour fast. For example, you might eat between 2:00 pm and 6:00 pm every day and fast for the other 20 hours. This would involve eating either one large, lengthy meal or two smaller meals within this period.

If you’re just starting out, you might just aim to have a 12-hour fasting period every day. That is, you would eat 3 meals a day from, say 7 am to 7 pm and refrain from eating anything from 7 pm to 7 am. At that point, you would ‘break your fast’ with a small breakfast. Truthfully, this isn’t even really fasting. It’s just NORMAL eating - this is how humans used to eat, back in the day before the food industry created the idea of snacking in order to get us to buy more food products.

Please note that there are some longer, multi-day fasts (longer than a week) that have been popularized over the last few years. There is very little, if any data, to support their safety or efficacy.

There isn’t one way to fast that is better than the others. And also, intermittent fasting may not be for everyone. If you are choosing to fast for longer periods of time over 20 hours it is important to check with your health care provider to ensure you are not at risk for fasting complications. Also, if you have diabetes and you’re on medications that can lower your blood sugar, you also need to have medical supervision to introduce fasting. 


During your fasting period you can consume water, broth, coffee, tea, any beverage with no sugar. Some fasting regimens allow up to 500 calories on a fasting day, but some will say that you really shouldn’t have anything at all. This is where there is some controversy.

 I also want to mention it is always okay to end the fast. Feelings of hunger are normal, but not feeling sick. If at any time there are feelings of nausea or dizziness, the fast should be ended with a light meal.


1.   Drink lots of water

2.   Stay busy

3.   Ride out the hunger waves (they are normally just at the beginning when starting)

4.   Give yourself a month to see if it is a good fit for you

5.   Don’t overeat/binge after fasting and make sure you have at least 50g of protein to help with feeling full.

6.   It’s important to follow a lower carb diet between fasting periods, as this will help reduce hunger making fasting easier, may also increase effect on weight loss.



The answer is no. Remember, when you’re working out your eating plan to manage your weight long term, the MOST IMPORTANT factor is finding a way of eating that you can be happy with forever. So if you decide you want to incorporate intermittent fasting, but this Saturday you are having brunch with your in-laws, well allow yourself the flexibility of eating earlier that day and just resume the next day. You need to have FLEXIBLE RESTRAINT. That is – you apply restraint with your eating, but you are flexible enough to live your life.

The main difference, as you may suspect, is that shorter fasting periods are less effective and are usually done more frequently. So a 16:8 fast is often done daily, whereas a 24 hr fasting period is done 2-3 times per week.


You can consume water, tea, coffee, or bone broth. Now I often get the question can you have milk, cream or sweeteners in these. There is little information on the sugar alcohols including xylitol. So I don’t really know if they are acceptable or not. However, when in doubt, my position is that these are not traditional, real foods, so best avoided. In terms of cream and milk, they are best to be avoid but for compliance sake 1-2 teaspoons of milk or cream is okay.


Physical activity is still recommended while IF. Begin with lighter intensity physical activity while you are starting, but if this feels fine it is extremely beneficial to build back up to regular intensity. Fasting is beneficial because it causes the depletion of glycogen stores and following that, the reliance on fat reserves for fuel. Exercise in the fasted state helps us deplete these stores faster.

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