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Clinical Dietitian's Two Cents: Intermittent Fasting

The Intermittent Fasting is another diet method that has caught on attention in recent years.

“I can eat whatever I want during my ‘feed’ Period but still lose weight, right? I ‘ll just sleep till noon and wake up during my ’feed’ period. Is that how it works?”




There are some Variations of IF:

1) Time-Restricted Feeding (TRF)

  • 8/6/4 hours feeding
  • 16/18/20 hours fasting


2) Alternate Day Fasting (ADF)

  • 25% energy needs on fast days
  • 125% energy needs on alternating “feast days”


3) 5:2 Diet

  • Fast (400-600kcal/day) on wo consecutive or non-consecutive days a week


4) Warrior Diet

  • Fast during the day and have one large meal at night


5) Eat Stop Eat

  •  Fast for 24 hours 1-2 days a week




Research on Alternate Day Fasting (ADF) vs daily energy restriction

RCT by Trepanowski et al. (2017) reported at 6 and 12 months that here is not significant difference between groups for blood pressure and heart rate, triglycerides, fasting glucose, fasting insulin & insulin resistance and C-reactive protein. Dropouts are greater in ADF group. The systematic review and meta-analysis of ADF trials concluded that ADF achieves weight loss but there was no evidence that it provided superior management in comparison to continuous energy restriction.


Research on 5:2 Diet vs daily energy restriction

Systemic review and meta analysis of RCTs found that similar weight loss and weight maintenance. There are the improvements with no difference between groups which are waits circumference, body fat mass, glucose & HbA1c, lipid profile and blood pressure. The dropout rate is similar and the feelings of hunger may be more pronounced during IF. This research concluded that both intermittent and continuous energy restriction achieved a comparable effect in promoting weight-loss and metabolic improvements.





Common Scenarios

“I didn’t eat breakfast. I can afford to eat a little more here and a little more there.”


You should still stick to your portions. A little here and a little there may add up and sometimes “little” is really not that little.


“Because I skipped breakfast, I’m hungry and everything on the menu looks so tempting!”


You should still make the healthier choice. Hunger significantly affects decision-making. A disadvantage of IF.


“Finished my meal in under 10 minutes because I was starving!”


Eating too quickly leads to overeating. Your stomach takes about 20 minutes to recognize fullness. Eat mindfully.


“I’m allowed to have this cake because its’s still within my eating time period.”


Weight loss will occur when there is calorie deficit. Eat within your targeted calories to see results. No, you can’t just eat everything and anything even though it is within the eating period.


‘I’m going to snack on this because I’m afraid I’ll get hungry when I fast this evening”


Yes, you may have healthy snacks between main meals. But, you do not need to be constantly snacking of finish the extra bag of nuts.


“Got to squeeze in another burger before 8pm!”


1 unit of calorie is still 1 unit of calorie whether it is 7.59pm or 8.01pm.


“Reduced non-exercise activity thermogenesis (NEAT) during fast. Examples of NEAT: getting up from the work desk, taking the stairs, standing, cleaning etc.”


People tend to move less during the fast. But just like how a little calorie intake here and there adds up, a little calorie expended here and there adds up too!


“I’m fasting so I don’t have much energy to workout today. I’ll skip my workout just for today (and tomorrow, and the day after…)”


Exercise is an important part of the weight loss equation. Both in creating a calorie deficit and preserving, if not increasing muscle mass during weight loss.





Does IF Bring Any Pros & Cons??



Last but not least, available evidence suggest that intermittent fasting produces equivalent weight loss compared to continuous energy restriction (when done correctly). That is, wen calorie restrictions are adhered to. Eat healthy and nutritionally balanced meals even when practicing IF. I highly doubt there will be results if you do not watch what you eat. With or without intermittent fasting, calorie deficit is required for weight loss. No calorie deficit, no weight loss.




Written by, 

Dietitian Ivy Cheah


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