Weight Loss

Intermittent Fasting Unveiled: Separating Facts from Fiction with a Registered Dietitian

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Intermittent fasting has been gaining popularity for years now because of the claims of “easy” weight loss by following a simple plan that requires very few food rules. So we ask, is it worth the hype?

Intermittent fasting (IF) is a pattern of eating that involves periods of eating followed by periods of fasting.

Different Approaches to Intermittent Fasting

There are several different approaches to intermittent fasting, but they all involve restricting the period of time that you eat during the day or week.

Some common methods of intermittent fasting include:

  • 5:2 diet- eat normally for 5 days and restrict your calories to 500-600 for the other 2 nonconsecutive days
  • 16/8 method- fast for 16 hours and eat during an 8-hour window (we see this most often and is much simpler so that is what we will focus on here)

What are the potential benefits of intermittent fasting?

Intermittent fasting has been claimed to have a number of potential health benefits, including:

  • Weight loss
  • Improved insulin sensitivity
  • Reduced inflammation
  • Improved cardiovascular health

In order to evaluate these claims, we looked at the latest research and came up with some surprising, and not-so-surprising answers.

There is no shortage of research on the topic, but until recently, there had been a lack of good quality long-term studies that included control groups. Previous research had mixed results, with many reporting positive outcomes for weight and other health risk factors.

However, without control groups that serve to compare intermittent fasting with more standard weight loss methods (such as simple calorie restriction), it has been difficult to understand if intermittent fasting would truly stack up better or worse than any other diet.

There were two recent studies that evaluated the intermittent fasting approach by following participants over longer periods of time.

The first study was a cohort study, which followed a group of 547 participants who tracked information about their meals and snacks, as well as food timing, over the course of 6 years.

Researchers concluded that those who had a shorter window of time between first and last meal, (those with longer daily fasting times) did not show any significant changes in weight.

What the study did show was that those who ate more frequent, higher calorie meals did gain weight over time. Meal timing alone did not produce significant weight loss in this group.

The second study was a controlled clinical trial where 154 participants in one group were asked to eat a calorie-controlled diet within a limited window each day (intermittent fasting group). The second was asked to eat the same calorie-controlled diet, but throughout the day during normal meal and snack times.

After one year, both groups lost about the same amount of weight, demonstrating that total energy intake, and not the time of day, determined the amount of weight lost. The scientists also found no differences in such risk factors as blood glucose levels, sensitivity to insulin, blood lipids or blood pressure.

Why does intermittent fasting seem to work for some people?

IF may work for some people due to a few different factors, with the biggest one being that, in practice, it is actually a calorie restriction diet. If someone is used to eating breakfast, and then snacking after dinner late into the evening and then suddenly stops the early morning and late eating, for example, eating only 11am – 7pm while changing nothing else about how much or what types of foods they eat, they are getting fewer overall calories during the day. Even if they increase the amount of food they are eating at lunch and dinner, they may not be increasing it enough to compensate for their otherwise typical late-night grazing.

Some people are drawn to IF because it is simple to follow (only one rule), they aren’t breakfast eaters to begin with, and they might already struggle with overeating late at night out of boredom or for comfort.

What are the drawbacks?

One of the pitfalls that we frequently see with our clients here at No Diet Dietitian is that skipping meals and snacks can lead to poor mood and energy, create a deficiency in the total amount of protein and other nutrients your body needs every day, and most importantly, it can lead to binging.

The restrict-binge cycle is one that we commonly see with people who have a history of dieting. Deprivation early in the day creates strong urges to later overeat (what we call “bottomless pit syndrome”) followed by physical discomfort, regret, a feeling of failure, and then the next day the restriction cycle begins all over again. This all-or-nothing dieting mentality never works, and keeps you stuck in a self-defeating cycle of “tomorrow I’ll do better”.

We advocate for feeding your body early in the day to help defeat this cycle. The evidence for muscle mass and metabolism very much supports a balanced high protein (20-40g) breakfast. If we’re missing out of this we’re missing out on building our metabolism and helping balance blood sugar and regulating hunger/satiety cues all day long.

This is our number one recommendation for clients with insulin resistance (Metabolic Syndrome, Type 2 Diabetes, PCOS). Rather than restricting food, we’re adding in great nutrition that fuels our morning and helps our body function better.

Intermittent fasting can become just another calorie restriction diet which, when done to the extreme, can be detrimental to metabolism and set people up for even more weight gain down the line.

People who have a history of eating disorders, chronic dieting, people with diabetes, and who are pregnant or wanting to become pregnant are not advised to follow this style of plan. If you are interested in a more holistic, non-diet approach to nutrition and weight loss with a plan tailored specifically to your health goals, please reach out to us today. Email Info@nodietdietitian.com or schedule a free discovery call.

Written by Christine Weiss RD, CD


Zhao D, Guallar E, et al. Association of Eating and Sleeping Intervals With Weight Change Over Time: The Daily24 Cohort. J Am Heart Assoc 2023; Jan 18:e026484.

Liu D, Huang Y, et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N Engl J Med 2022; 386:1495-1504.