Some note on Intermittent Fasting (IF)

1. Does IF work?

IF researches have been done mostly on fat rats. Initial studies in humans have shown that IF is safe and effective, but no more effective than any other diet (Monique Tello, 2018) [1]. That means, fasting every other day and eating less every day both work about equally for weight loss. IF is just harder to follow.

It is effective …

On a recent study by researchers from University of Alabama on small group of obese men showed that the eight-hour IF (all meals fit in to early 8-hour period of the day, 7am-3pm) group and the 12-hours group (7am-7pm) both maintained same weight, but the 8-hours group had dramatically lower insulin level and significantly improved insulin sensitivity, significant lower blood pressure. The 8-hour group also had significantly decreased appetite [2].

… But with some conditions

So the conclusion is IF, when combined with a healthy diet and lifestyle, can be effective for weight loss, especially for people at risk for diabetes. However people with advanced diabetes or on medications for diabetes, pregnant or breastfeeding women should not attempt IF unless under the close supervision of a physician.

However, there are not many evidence about how well IF works over the long term. Unlike the Mediterranean or the vegetarian diet, which both links to healthy heart and healthy body size.

And IF is not more effective than the other diets

A systematic review of 40 studies [6] found that IF was effective for weight loss. A brief summary of their findings:
- Dropout rate ranged from 0–65%. IF doesn’t show low dropout rate, therefore was not necessarily easier to follow than other weight loss approaches.
- No significant difference in weight loss, weight regain, body composition compare to the continuous calorie restriction or usual lifestyle group

A RCT research [5] followed 100 obese individuals for 1 year did not find IF to be more effective than daily calorie restriction:
- no significant differences in BP, heart rate, fasting glucose, fasting insulin
- No significant difference in weight loss, weight regain, body composition
- At 12 months, IF group show significantly increased LDL cholesterol (bad cholesterol) level
- IF group has higher dropout rate (38%) compares to other groups (29%)

2. How does it work?

The entire idea of IF is to allow the insulin levels to go down far enough and for long enough that we burn off our fat (Monique Tello, 2018) [1].
Insulin helps bringing sugar into the fat cells and store it there, when insulin levels go down, these fat cells will release stored sugar to be used as energy.

3. Risks

• IF might make you feel sick: headaches, lethargy, crankiness, constipation
• IF is hard for those who snack often. Risks for overeating when food is allowed, might foster unhealthy behaviors such as an increased fixation on food.
• May cause older adults to lose too much weight, which can affect bones, overall immune system, and energy level.
• There is less evidence about how IF might affect older adults since most of the studies only looked at small groups of young or middle-aged adults, for only short periods of time

4. How to do it effectively?

In case you still insist on trying IF:
- Avoid sugars and refined grains. Instead eat fruits, vegetables, whole grains, lean proteins, healthy fats.
- Don’t snack between meals
- Use a simple form of IF (limit the hours of the day when you eat, make it earlier in the day: 7am — 3pm, or 10am — 6pm)
- Avoid eating at night time.

An RCT study [3] showed that with unhealthy IF, people still might not lose weight, instead they lose a lot of muscle mass. So sticking to a healthy diet is the key important for any diet. IF is just a tool.

Make sure to discuss with your doctor first. Skipping meals and severely limiting calories can be dangerous for people with certain conditions, such as diabetes.

Individuals with the following conditions should abstain from intermittent fasting:

- Diabetes
- Eating disorders that involve unhealthy self-restriction (anorexia or bulimia nervosa)
- Use of medications that require food intake
- Active growth stage, such as in adolescents
- Pregnancy, breastfeeding

Conclusions

• Yes, it works. But only if you still eat healthy. IF is just a tool, sticking to healthy diet, drink enough water, exercises regularly are still necessary. Without that, IF might give you more risks than benefits.
• But not better than other methods (reduce daily calories)
• It has some risks which we don’t understand fully yet. More high qualities studies including RCT with follow-up of more than 1 year are needed. Strong recommendations on intermittent fasting for weight loss cannot be made at this time.
• Check with your doctor before trying it out

The best diets (no risk, multiple health benefits, proven for long time) are still the balance diet recommended popularly, or the Mediterranean or the vegetarian diet. If you are looking at losing weight, still eat healthy as one of these diets suggest, simply cut calories (down to ~75% daily) and add on with regular exercises. Stop looking at trends!

[1] Monique Tello, MD, Massachusetts General Hospital. June 2018 https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156
[2] https://www.sciencedirect.com/science/article/pii/S1550413118302535
[3] https://pubmed.ncbi.nlm.nih.gov/32986097/
[4] https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/
[5] Trepanowski JF, Kroeger CM, Barnosky A, Klempel MC, Bhutani S, Hoddy KK, Gabel K, Freels S, Rigdon J, Rood J, Ravussin E. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine. 2017 May 1.
[6] Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA, Hills AP, Wood RE, King NA, Byrne NM, Sainsbury A. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418:153–72