Intermittent Fasting: A Physician’s Perspective

I started intermittent fasting (IF) five months ago while researching the topic for a lecture that I was to give. I must say, as someone who grew up in a poor country where voluntarily turning food away is a blasphemy, I was impressed by the numerous benefits reported in scientific literature on IF. I gave time-restricted feeding a try and was surprised to find how quickly my body adapted to the torture of not eating for 16-18 hours. In this article, I hope to give you some background and guidance on IF, and how to do it safely especially if you have diabetes.

How Is Intermittent Fasting (IF) Different From Calorie Reduction (CR)?

Calorie reduction is reducing the total daily caloric intake. Studies have shown that CR without malnutrition leads to reduction in body weight and extending lifespan across animal models (both primate and non-primate). Studies in humans have also shown that calorie reduction lead to better cardiovascular health, insulin sensitivity, mitochondrial function, and cognition. But the same studies have shown that people have a difficult time sustaining continuous calorie reduction over time.

Intermittent fasting (IF) has gained popularity as an alternate to continuous calorie reduction. IF is more user-friendly since there are many ways to go about doing this without having to reduce total calories. The goal of IF is to fast long enough to make ketones (more on that later) which are considered a “super fuel” with multiple benefits on longevity, inflammation, cognition, cardiovascular health, obesity, etc.

How does IF work?

Most of us fast every night for at least 10-12 hours if we truly stop eating at least 3-4 hours before bedtime. Unlike the hunter-gatherer times, we are both blessed and cursed with electricity and easy access to food, which keeps us up longer, eating longer. This causes a number of disadvantages to our health. After a meal, we have plenty of sugars (glucose/carbohydrates) to use as fuel. But as we fast, we run out of these sugars and then start breaking down the stored sugars (i.e. glycogen). Once these glucose stores are depleted, our bodies turn to fat breakdown (as opposed to breaking down proteins, which our bodies need to save).  Some of these fats are also sent to the liver to make ketones, which have many downstream benefits that I will describe below. In general, it takes about 12-36 hours of fasting to make ketones. The time is variable since it depends on the time from your last meal, how large that meal was (how much glucose you have floating around), and how much stored glucose is in your liver.

What Types of IF Regimens Could You Try?
  1. Time-Restricted Feeding (or fasting): Fasting for various periods of time, typically 12 hours or longer and eating normally during the rest of the time. For example, fasting for 16-17 hours and eating for 7-8 hours
  2. Alternate-Day Modified Fasting: 5:2 intermittent fasting is commonly used when you have 5 days of normal eating with 2 days of 500-1000 calories/day
  3. Alternate-Day Fasting: Alternating a 24-hour fasting day with a normal feeding day
  4. Periodic Fasting: Fasting 1-2 days/week and eating as usual 5-6 days/week
What Are the Benefits?

The obvious benefit that I noticed was a decrease in my appetite. At first, I felt compelled to eat my own arm. But after few weeks, my body got used to this routine and now most days I do not feel the need to eat until around noon. I also do not experience night-time cravings and my sleep has improved.

Other Benefits Seen in Literature, in No Particular Order:
  • IF, in contrast to CR, helps preserve muscle mass while losing fat mass. This is important for any athletes out there.
  • Better regulation of circadian rhythm (sleep, wake cycle) especially when eating is restricted to earlier parts of the day.
  • Reduction in inflammation (studies show markers associated with inflammation decrease and anti-inflammatory markers increase).
  • Improvement in insulin sensitivity.
  • Improved memory in patients at risk for Alzheimer’s disease and memory problems.
  • A 2019 UCSD pilot study of patients with metabolic syndrome (diabetes, high cholesterol, high blood pressure) on 10 hours/day time-restricted eating showed reduced blood pressure, belly fat, weight, cholesterol and blood sugars.
What Are Some Side Effects?

There are not many side effects with IF except some irritability from being “hangry.” This disappears with time. Extended fasts can be unhealthy and can lead to nausea/vomiting and nutritional deficiencies. Also, data is mixed on the effects of IF on patients with active cancer.

What Are the Implications for T1D and T2D with IF?

The topic of ketones and their association with ketoacidosis can bring up unpleasant memories to folks with T1D. But, with IF, we are talking about a lot less ketone body production than what you would get with diabetic ketoacidosis (DKA). For people on medications called SGLT2 inhibitors (Empagliflozin, Canagliflozin, or Dapagliflozin), discuss with your endocrinologist before any attempt at IF since there could be increased risk of ketoacidosis. You might also notice that adjustment of your basal insulin is needed during fasting.


Intermittent fasting is best summarized by a quote from Mark Twain, who wrote, “A little starvation can really do more for the average sick man than can the best medicines and the best doctors. I do not mean a restricted diet; I mean total abstention from food for one or two days.”


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    Thanks for this. I had to change my work schedule for Covid at first. Worked 10 weeks of 3:00-1130 to relieve usage on my healthcare related secure network during the day. It had a hand in Covid weight gain & all the side effects. I want to try this & so will ask my doctor.

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      If you do decide to try it, let us know what you think. Changing work schedules is tough – good luck and be well!

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    I love IF! I switch it up almost every day to keep my metabolism “guessing”, if you would. The only downside is, I drink more water…aka more trips to the bathroom! lol!

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