Dietitian-Approved: Intermittent Fasting for Weight Loss


Last Updated on December 16, 2022 by Kayla

Dietitians are trained skeptics – especially when it comes to fad diets. Initially, I wrote intermittent fasting off as just that – another fad diet meant to come and go just like the others, yet I continued to be questioned by patients, family, and friends on a regular basis about the topic.

As a registered dietitian, I strive to be a one-stop shop for answers to patient’s nutrition-related questions, and I felt completely inadequate to answer their inquiries related to intermittent fasting. I really didn’t know enough about it, and quite frankly, it never came up once during my four years of undergraduate training or 1500+ hours of clinical practice. And so, I started digging into the research.

I searched medical journals and peer-reviewed research papers hoping to confirm my doubts about what I thought was another fad diet. To my surprise, as I began to uncover the physiology of intermittent fasting, it clicked. Having taken many science-based classes during my undergrad education, I was able to understand the physiology of intermittent fasting and recognize the prejudgements I had made against it.

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Insulin Response & Weight Gain

My “ah-ha” moment was when I realized that intermittent fasting is about managing your body’s response to insulin – not starving yourself.

Insulin, a hormone made by the pancreas, is responsible for how your body’s cells obtain energy. Often referred to as a “lock and key” mechanism, insulin “unlocks” cells allowing glucose to enter from the bloodstream.

After a meal, your body breaks down food into glucose molecules. Subsequently, insulin is released to help aid the transfer of energy from blood to cells. When there is “excess” or more than what your body immediately requires {like after a large meal}, insulin helps package away extra energy as fat – a neccessity for our survival. Without insulin, blood sugar remains high and the body cannot access energy.

Blood sugar, and ultimately insulin, is impacted by the foods we eat and our liver. When blood sugar rises, so does insulin. The key here is that without insulin, your body cannot store fat. Let me repeat that, no insulin = no fat storage.

Why eating every 2-3 hours is NOT the solution to weight loss

When a person eats three meals and multiple snacks per day, they are essentially fueled by a constant drip of food. This translates to multiple upticks in blood sugar levels, and what else? You got that right – a steady surge of insulin.

Simply put, more food, more often = increased blood sugar = increased insulin exposure = fat storage.

To complicate matters more, our bodies can become insulin resistant when exposed to insulin more often and at higher levels.

Think of caffeine, for example. You start with one cup of coffee. Initially, you feel the effects of caffeine and relish in the extra perkiness. Over time, this “perk” starts to diminish, so you add a second cup of coffee. Then a third, and maybe even a fourth cup. Your body builds a tolerance to caffeine, and more coffee is needed to obtain the same small perk you enjoyed when you first started drinking it.

In a similar way, our body’s reaction to food – specifically {highly processed} carbohydrates and proteins – is to release insulin. Furthermore, with more frequent eating occasions {such as snacking between meals}, insulin release is increased and our body begins to build tolerance toward insulin with more exposure – similar to how a person’s caffeine tolerance increases.

Over time, a person’s body requires more and more insulin to compensate. This, my friends, is insulin resistance which is the primary cause of type 2 diabetes.

So then what? How do we fix it?

The answer is simply – intermittent fasting – or in other words, a temporary break from food, and further, insulin.

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The Solution: Intermittent Fasting (or Timed Eating)

Intermittent fasting can be done in many ways, and essentially, it involves reducing your body’s exposure to food, and subsequently, insulin.

Think of the earlier example with caffeine. To decrease caffeine tolerance {so you’re able to feel the affect after just one cup}, you might limit or completely omit coffee for a period of time.

Similarly, you can maximize weight loss and insulin sensitivity {and limit fat storage} by (1) limiting your exposure to food, and (2) recognize that some foods have a greater impact on blood sugar and insulin levels than others.

This pause from food allows your body to reset its defaults, increase insulin sensitivity, and tap into stored fat for energy. Moreover, when it does come time to enjoy food, your body is better able to handle the workload.

Bottom line: Intermittent fasting works for weight loss because it minimizes your body’s exposure to insulin which essentially is our “storage” hormone.

Intermittent fasting has many other health benefits including reduced inflammation, decreased blood pressure, improved mental focus, and autophagy {a fancy term for cellular clean up of old and damaged cells}.

Flexible fasting

Finding a fasting routine that suites you involves trial and error. It’s important to remember that everyone’s intermittent fasting experience is different, and what works for one person may not work for another. It’s not one-size-fits-all.

“Clean” or “dirty” intermittent fasting, 16:8, OMAD, the jargon can be intimidating at first. Step one for many people starts with three square meals a day and limiting/omitting snacking in between. From there, you can wiggle down your eating window to 12, 10, 8 or even 6 hours – whatever you find works best for you.

If you are new to intermittent fasting, be patient with yourself and tune into your body’s hunger and fullness cues. You might eat because “I know I should eat breakfast”, for instance, or because a family member is snacking and now you want to eat too – not because of true hunger but out of environmental or emotional cues.

It takes time to reestablish these connections, and you might fear being hungry. I assure you this feeling will pass, and you will learn to free your mind of food and use the extra energy {and grocery savings!} on other precious pasttimes.

While the health benefits reach far beyond weight loss, I recognize it isn’t for everyone. As a registered dietitian who supports and practices intermittent fasting, it’s simply on my heart to share this practical tool for those struggling with their weight and/or their relationship with food.

If you would like to read further about intermitent fasting, insulin, and weight loss, I compiled a list of my favorite intermittent fasting books.

Please comment below with any feedback, questions, or comments regarding intermittent fasting. I would love to hear from you!

Yours truly,

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