The Pros and Cons of Intermittent Fasting

By now, many of you have likely heard of, and maybe even tried, intermittent fasting. This approach has surfaced as one of the trendiest weight-loss techniques in the last several years. As with all fad diets, we hope you’re wondering the following before trying them out:

  1. Is it safe? Should I talk to my doctor or a dietitian first?
  2. Is there any research backing  up its efficacy? Is all of that fasting going to be worth it for my health goals?
  3. Is it right for me? Can I, and do I truly want to, fit this type of diet into my lifestyle?

As with many trendy fad diets, the answer is a resounding “Maybe. But…”

Intermittent fasting (IF) is what it sounds like: alternating cycles of eating and fasting (clear, calorie-free liquids are okay during fasts). There are a few different approaches you can take to this:

  •  16/8 – Fast for 16 hours per day, with an 8 hour window for eating every day. Aim to eat earlier in the day (7am-3pm or 10am-6pm) to avoid eating and snacking close to bedtime. Some people who find that they’re not usually hungry in the morning tend to gravitate towards a later schedule, starting their first meal of the day with lunch and eating until about 8:00pm.
  • 5:2 – Two days per week, limit calorie intake to 500-600 calories.
  • Eat-stop-eat – Once or twice per week, do not eat for 24 hours. Generally, one would eat a meal like breakfast and then not eat again until that same meal 24 hours later. 
  • Feast vs Fast – Alternate days of eating 25% of your total calorie needs with days where you eat  125% of your total calorie needs.

These methods are safe for most people and can generally do more good than harm. However, there are certain individuals, such as people with diabetes on medications that can cause low blood sugar (i.e. insulin or sulfonylureas), that we recommend talking with your doctor first before trying IF. 

IF has been found to be an effective weight loss tool if it’s sustainable. But many individuals find that fasting is challenging to stick with, as you could imagine. If you’re interested in trying IF, we recommend starting out with the 16/8 approach because it is simple, requires a small shift to your normal routine (you’ll likely just have to shift your breakfast later by a few hours and limit late night snacking), and lines up with our circadian rhythms. While IF can lead to weight loss, it may not cause greater weight loss than traditional daily calorie restriction. So if weight loss is your goal, go with what suits you best. 

However, the buzz around IF also includes findings that it can reduce insulin resistance, and possibly inflammation, as well as other risk factors for chronic diseases. Studies found that levels of the protein TPM3 were higher in those who had been practicing 15 hours of fasting per day than those who had not. TPM3 helps improve the body’s sensitivity to insulin and repair damaged cells that may have become insulin resistant. If diabetes runs in your family or your doctor has mentioned that you’re at risk for developing or already have prediabetes, fasting may offer you more benefits than standard calorie restriction. 


  • It may be an effective weight loss technique
  • There are other possible health benefits (insulin sensitivity, reduced inflammation, etc.)
  • A variety of approaches can work
  • A change to what you are eating is not required, just when


  • Fasting may not be doable or sustainable for everyone
  • May not be safe for people who already have diabetes, are pregnant, or have a history of eating disorders
  • Research can be confusing to draw conclusions from since there are so many versions of fasting
  • There is a need for long-term studies to be done

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