How does Intermittent Fasting Cause Weight Loss?

We’re currently seeing a virtual epidemic of obesity worldwide, with 33% of our population estimated to be obese as of 2018​1​. This amounts to a staggering 44.2 crore obese Indians. India isn’t alone in this with healthy weight individuals now a minority in the US​2​, for example.

We could go on about the causes of the situation we find ourselves in, the initiatives that could help in reducing obesity among or population and so on. The subject of this post however, is how does Intermittent Fasting (IF) cause weight loss.

Intermittent Fasting has been found to aid in weight loss, blood sugar management, alleviate hypertension, improve depressive symptoms, address inflammatory conditions and so on. In this post, we’ll take a high level look at how IF aids weight loss.

Consider the following normal scenario for most of us:​3–5​

  1. Eating regular meals causes an insulin response in our bodies.
  2. The body then proceeds to break down our foods into its various components, the sugars, as glucose going to cellular storage as well as glycogen stores in our liver. Depending on how much we’re eating and how much of that food energy we’re using, glucose may also be converted to fat and be added to body fat stores.
  3. Insulin instructs our bodies to use glucose, and not fat, for energy.
  4. The body proceeds to use glucose from cellular storage for its needs.
  5. Fat stores remain largely untouched.
  6. Somewhere in between, we eat something or the other again, maybe a snack or a regular meal. Most probably we haven’t really used all the food energy ingested from the last meal.
  7. The cycle starts from step 1 again, with our bodies slowly accumulating fat, and using none or little of it.

Now consider how normal weight loss recommendations work.

  1. We eat a reduced number of calories than our bodies are likely to burn.
  2. Some weight loss begins happening after a while.
  3. Also, after a while, our bodies reduce their energy requirements to the amount being eaten.​6,7​
  4. Weight loss stops happening, since the amount being eaten is equal to the amount being burnt.
  5. We try and reduce calories further; the body also adjusts, by bringing down its metabolic rate.

So, we’ve reduced our metabolic burn, which is very difficult to bring up again, without gaining more weight, possibly lost some degree of body function and now put on weight faster than ever, because those reduced calorie meals are difficult to sustain, and when we go back to eating normally, the excess unused energy gets stored as fat. Also, with most people, getting all their required nutrition with reduced calorie diets, is a real challenge.

This is also why most people are unable to lose weight with exercise, given they tend to eat something before and after exercising, signalling the body to use glucose and not fat, for its energy requirements.

With Intermittent Fasting, we’re eating our usual quota of calories, but less frequently. So what happens is as follows, with the first 5 steps being exactly the same as earlier.​3–5​

  1. Eating regular meals causes an insulin response in our bodies.
  2. The body then proceeds to break down our foods into its various components, the sugars, as glucose going to cellular storage as well as glycogen stores in our liver. Depending on how much we’re eating and how much of that food energy we’re using, glucose may also be converted to fat and be added to body fat stores.
  3. Insulin instructs our bodies to use glucose, and not fat, for energy.
  4. The body proceeds to use glucose from cellular storage for its needs.
  5. Fat stores remain largely untouched.
  6. We continue fasting and when the body needs energy, and cellular storage of glucose is exhausted, it draws glucose by converting glycogen from the liver.
  7. When glycogen stores too are exhausted and we still haven’t eaten, and there’s no/little insulin around, the body then turns to fat storage, using ketones instead of glucose for energy, and continues doing so, until we eat something and go back to step one. Some parts of our bodies need glucose, which is created by the liver.
  8. So, the longer we’re fasting, after our glucose reserves are exhausted, the more weight we’re losing.
  9. If we exercise during this period, the more fat we’re burning.​8​
  10. We then eat as per our body’s metabolic needs, all of which gets used up as it should, and start the cycle again from step 1.

The above is an approximation of what is a complex, multi-cycle, multi-component process. What we’re essentially doing, is encouraging the body to switch to fat as a source of energy, and then supplying it with the just the right amount of energy it needs via food, all of which is used, so there’s no contribution to fat stores and then repeating the cycle to burn fat again, without eating any less than we need to.

  1. 1.
    Babu G, Murthy G, Ana Y, et al. Association of obesity with hypertension and type 2 diabetes mellitus in India: A meta-analysis of observational studies. World J Diabetes. 2018;9(1):40-52. doi:10.4239/wjd.v9.i1.40
  2. 2.
    Rynders C, Thomas E, Zaman A, Pan Z, Catenacci V, Melanson E. Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients. 2019;11(10). doi:10.3390/nu11102442
  3. 3.
    Petersen M, Shulman G. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev. 2018;98(4):2133-2223. doi:10.1152/physrev.00063.2017
  4. 4.
    Smith R, Soeters M, Wüst R, Houtkooper R. Metabolic Flexibility as an Adaptation to Energy Resources and Requirements in Health and Disease. Endocr Rev. 2018;39(4):489-517. doi:10.1210/er.2017-00211
  5. 5.
    Goodpaster B, Sparks L. Metabolic Flexibility in Health and Disease. Cell Metab. 2017;25(5):1027-1036. doi:10.1016/j.cmet.2017.04.015
  6. 6.
    Redman L, Smith S, Burton J, Martin C, Il’yasova D, Ravussin E. Metabolic Slowing and Reduced Oxidative Damage with Sustained Caloric Restriction Support the Rate of Living and Oxidative Damage Theories of Aging. Cell Metab. 2018;27(4):805-815.e4. doi:10.1016/j.cmet.2018.02.019
  7. 7.
    Mitchell S, Tang Z, Kerbois C, et al. The effects of graded levels of calorie restriction: VIII. Impact of short term calorie and protein restriction on basal metabolic rate in the C57BL/6 mouse. Oncotarget. 2017;8(11):17453-17474. doi:10.18632/oncotarget.15294
  8. 8.
    Cox P, Clarke K. Acute nutritional ketosis: implications for exercise performance and metabolism. Extrem Physiol Med. 2014;3:17. doi:10.1186/2046-7648-3-17

3 thoughts on “How does Intermittent Fasting Cause Weight Loss?

    1. Unless you’re on strong diabetic medication or Insulin, chances are IF can help. If you are on strong medication, IF can still help, but you’ll need to follow a protocol to ensure your blood sugar levels are monitored and in a safe range.

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