Intermittent Fasting for Metabolic Rate and Weight Loss

Fasting benefits for insulin resistance and metabolic rate - not calorie restriction

If you get the majority of your health information from fitness and wellness influencers on Instagram or TikTok, you might be getting misinformation about intermittent fasting benefits.

When done properly, fasting and intermittent fasting will improve insulin resistance, metabolic rate, and metabolic flexibility, regardless of the number of calories consumed before and after fasting. If you think of fasting as an easy way to achieve a calorie deficit, think again.

Hi friends. I’m Hilary Beckwith, ex-dieter and holistic nutrition expert. Clients come to see me with signs of adrenal stress and inflammatory conditions, and my job is to find the root causes so we can address their symptoms more effectively and fill in the gaps between what their doctor is saying and what their body is saying. Click here to read my Medical Disclaimer.

In this article, you’ll learn:

• the difference between calorie deficit and intermittent fasting

• physiological effects of fasting

• different types of fasting

• what should you eat to break your fast?

• who should not practice fasting?

---

isn’t fasting just another way to restrict calories?

Yes and no.

The research behind fasting and metabolic rate tells us two main key points:

1. chronic calorie restriction (dieting) slows metabolism over time [1,2], and

2. the chronic presence of insulin slows metabolism, causes weight gain, and increases insulin resistance [3,4]

And since insulin is released in times of feeding, especially carbohydrates (fibers, starches, and sugars), it can be said that calorie restriction is a part of the world of fasting benefits - but not for the sake of achieving a calorie deficit.

EXAMPLES OF CALORIE RESTRICTION V. FASTING FOR INSULIN RESISTANCE

SCENARIO #1: Using the Calorie Restriction (Dieting) Method for Weight Loss

You decide to use the calorie deficit method for weight loss, meaning, the calories you burn must be more than the calories you consume. This requires avid tracking on your part, a constant attention to calorie count and scale numbers, and even then you are missing important data - your total energy expenditure, which varies widely from person to person, and requires a very specialized type of testing.

You increase calorie burn at the gym, and decrease calorie consumption. You track it meticulously using calorie deficit calculators and apps, and find you lose weight for the first 3-4 weeks of doing it. Then you plateau - even when in a calorie deficit, you find the weight is not shedding as easily as it once was. You become discouraged and irritable, and decide to “give in” when things aren’t working any longer.

SCENARIO #2: Intermittent Fasting for Metabolic Rate and Insulin Resistance

You decide to use intermittent fasting (we’ll talk about terminology and semantics later in the post) as a weight loss tool, applying a method commonly known as “16/8”, wherein you consume all your calories within an 8-hour window of time, with nothing but water for the remaining 16 hours of a 24-hour day. You don’t necessarily consume fewer calories, but find that your weight sheds at a slower, more consistent rate, and doesn’t plateau like it does with calorie restriction. You enjoy foods more because you’re eating the calories your body needs, and not restricting food types. You’re not tracking calories, not obsessively looking at numbers on an app or nutrition label. This feels sustainable.

The two main talking points we’ll return to throughout this article are:

• the quality of the calorie matters

• the timing of calorie consumption matters

• your body’s long-term metabolic response to fasting requires time and consistency - one day of fasting is not enough to magically boost your body’s metabolic rate, even if you begin to see weight loss results

how fasting works

In a nutshell, when fasting is done well, the intention of fasting is to reduce the amount of insulin being released into your bloodstream by eliminating food intake for a period of time.

With time and consistency, this method can help improve insulin sensitivity (more on this) and improve your body’s ability to use fat stores when glucose is not readily available. Put differently, proper fasting increases metabolism and improves your body’s ability to burn fat.

To understand how this works, we need to look at how metabolism works. Take a look at the diagram below.

Here are a few key points to understand before we move on to different types of fasting:

• WHAT IS METABOLISM?: Metabolism, specifically glucose metabolism, is a cascade of events that converts glucose into energy (ATP or Adenosine TriPhosphate). The process occurs inside of cells, and heavily involves the mitochondria, known as the “powerhouse of the cell” for this very reason - it very literally supplies the power that your cells and body need to function. Your body prioritizes carbohydrates for metabolism, but can also use proteins or fats when resources are present. Because converting fats and protein into ATP requires more energy, the body prioritizes carbohydrate sources of glucose.

• WHAT IS GLUCOSE?: Glucose is the molecular form of sugar. Put differently, glucose is sugar in its most broken-down form. Glucose comes primarily from carbohydrates, including starches, sugars, and fiber.

• WHAT IS INSULIN?: Insulin is a hormone produced by the pancreas when glucose is present. Insulin acts as a keyholder to cells - when glucose is present, insulin binds to the glucose molecule, shuttles it to the cell, and unlocks the proverbial door, allowing the glucose to enter and be converted to ATP by the mitochondria.

• WHAT IS INSULIN RESISTANCE?: When your cells are consistently exposed to more glucose than they can handle, they begin deactivating insulin receptors - if insulin is a key holder, and insulin receptors are the doors to the cell, picture the insulin receptors being boarded up with signs that say “KEEP OUT!”.

• Insulin resistance is typically the long-term result of diets low in whole food fiber, high in refined carbohydrates, and snacking or grazing often.

• Insulin resistance is common in women with PCOS, hence the belly weight, sugar cravings, and “hangry” symptoms.

• In the case of insulin resistance, glucose cannot enter cells to create fuel. The body produces even more insulin in an effort to get the glucose into cells (which does not work).

• With or without insulin resistance, any remaining glucose after cells have had their fill gets converted into glycogen (liver storage of glucose) and triglycerides, which get stored as fat tissue.

• Improving insulin sensitivity helps your body metabolize glucose more effectively and improves your ability to use fat as a secondary fuel source when glucose is not present. Proper fasting helps improve insulin sensitivity.

---

types of fasting

As we’ve discussed, fasting is not merely calorie restriction. What you eat before and after fasting, and the timing and quality of your daily meals, are also important factors when it comes to fasting for insulin resistance.

But let’s talk about different fasting terms first, so you can be on the same page as your health practitioners. You can see my earlier writings on fasting benefits here.

• INTERMITTENT FASTING: This term is commonly used incorrectly to refer to Time-Restricted Feeding. Here is the correct use of this term: Intermittent Fasting, also known as Alternate-Day Fasting, refers to a water-only fast for 24-72 hours, with careful attention to refeeding after each fast.

• TIME-RESTRICTED FEEDING: Again, often mistaken for Intermittent Fasting, but they are two different fasting methods. Time-Restricted Feeding allows you to eat daily, consuming all your calories within a set window of time. Sometimes referred to using the number of hours chosen to consume calories, such as “16/8”, meaning you’d consume all your calories within an 8-hour window, while taking in nothing but water for 16 hours.

• EXTENDED FASTING: Water-only fasting that lasts longer than 72 hours.

---

what should you eat after fasting?

There’s an abundance of poorly researched papers written regarding the long-term effects of fasting. But there’s some really great ones, too, and from credible sources. Many of these studies are discussed in Jason Fung’s The Obesity Code [5].

Some practitioners and influencers across the internet are touting that fasting benefits don’t last once you stop. Here’s why they have it wrong:

Studies that suggest this conclusion also do not disclose the eating and activity habits of the subjects. A study that observes this outcome, but does not provide clear data on all related factors (I would argue that what and when the subject eats is an important determining factor), is not a credible resource.

That said, a regular diet of starches, sugars, and processed foods is bound to undo any work you do with fasting, but the research on fasting benefits is clear:

Water fasting improves insulin sensitivity, increases growth hormone (which also protects from protein degradation), and increases metabolism. You can’t expect to stay healthy on a diet of processed foods, no matter how frequently you fast.

Below are my generally recommended food guidelines for post-fasting, but it’s important to remember that every individual has unique food and macronutrient needs, based on their biochemical composition and unique health goals.

WHAT TO EAT AFTER FASTING:

• choose whole foods

• prioritize fat, protein, and fiber

• avoid highly marketed “health food” labels, like “gluten-free”, “plant-based”, or “[number] essential vitamins” - these are not health foods, and are often highly processed (click here to learn how to spot health scams and confidently read food labels)

• don’t be afraid to consume more calories in your fast-break meal than you would typically, but use these techniques to help you avoid overeating:

  • eat while seated

  • take a few long, deep breaths through your nose before taking your first bite

  • take small bites and chew thoroughly (read why this matters)

  • mindfully eating improves digestion and helps you to listen to when your body is satisfied

MEAL IDEAS FOR POST-FASTING:

• Mediterranean Scramble - 3 scrambled eggs, 4-5 olives, 3 ounces plain whole-milk yogurt, and crumbled feta over a handful of chopped, sauteed greens (dandelion, chard, kale, broccolini, beet greens).

• Broiled Salmon and Green Vegetable - 5-ounce salmon filet cooked and seasoned to your liking, paired with roasted broccoli, stir-fried asparagus, or sautéed greens. Top with sauerkraut, yogurt, or avocado.

• Avocado “Toast” with Poached Eggs and Shredded Beef - Two thin slices of sweet potato baked until tender. Top with mashed avocado, sprouts, 2 poached eggs, and a generous scoop of leftover shredded beef.

While the health benefits of fasting are meaningful, fasting should not be practiced by everyone, and should always be practiced under the supervision of a qualified healthcare practitioner.

If you want to explore fasting for weight loss or metabolic health, click here to book a free consultation so we can talk about it.

---

was this helpful?

What’s your experience with fasting? Have you found any benefit from fasting?

Share your thoughts and questions in the comments below!

NUTRITION SERVICES

• Private Coaching

• Functional Lab Testing

• One-Time Assessment

---

MORE RESOURCES

---

BLOG REFERENCES

1. Zauner, C., Schneeweiss, B., Kranz, A., Madl, C., Ratheiser, K., Kramer, L., Roth, E., Schneider, B., & Lenz, K. (2000). Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. The American journal of clinical nutrition, 71(6), 1511–1515. https://doi.org/10.1093/ajcn/71.6.1511

2. Most, J., & Redman, L. M. (2020). Impact of calorie restriction on energy metabolism in humans. Experimental gerontology, 133, 110875. https://doi.org/10.1016/j.exger.2020.110875

3. Kolb, Hubert, et al. “Insulin Translates Unfavourable Lifestyle into Obesity - BMC Medicine.” BioMed Central, BioMed Central, 13 Dec. 2018, bmcmedicine.biomedcentral.com/articles/10.1186/s12916-018-1225-1.

4. Kahn, B. B., & Flier, J. S. (2000). Obesity and insulin resistance. The Journal of clinical investigation, 106(4), 473–481. https://doi.org/10.1172/JCI10842

5. Fung, J. (2016). The Obesity Code: Unlocking the Secrets of Weight Loss. Greystone Books.