Intermittent fasting (time-restricted eating.) Is it efficacious as a tool?

On September 28th, 2020 The Journal of the American Medical Association (JAMA) released a randomized control trial paper on time-restricted eating, or 16:8 intermittent fasting (see paper HERE.) One of the authors of the paper, Ethan Weiss is a fan of intermittent fasting (IF) doing 16/8 time-restricted eating for the past 6 years (likewise, I’ve been doing it for the past 8 years) so I’m sure he too was hoping for a better outcome. That said, there are unanswered questions, as I do feel that there are some major study design limitations and further research needs to be done.

Study details summary: 

Researchers at UC San Francisco conducted a 12-week randomized clinical trial to determine weight loss & metabolic risk markers. They recruited 116 participants men & women aged 18 – 64 years. Click the link above for the paper for more details. They did not assess IF benefits on neurological and cognitive benefits such as autophagy, or BDNF.  


  • The intermittent fasting group lost approx 2.5-3lbs, which was only marginal compared to the control group (not doing 16:8 IF.)  Most alarmingly is that the weight that the intervention group lost was muscle mass & not fat mass!
  • The study found no significant difference between the intervention & control group in total weight loss or other markers, such as fat mass, lean mass, fasting insulin or glucose, HbA1C levels, energy intake, or resting energy expenditure.  

Limitations with this study include: The study did not disclose what the IF intervention group were eating during their 8-hour feeding window, or whether they exercised. Also, the 12-8 pm eating window contradicts compelling previous research that eating earlier in the day and finishing earlier (syncing with our circadian rhythm – eat like a grandma) is optimal for weight loss and optimizing metabolic markers. This is when our metabolism is primed. 

Strength training & protein intake for muscle mass 

Building lean muscle mass is the best way we can help to prevent age-related disease and promote longevity. Low muscle mass has been associated with higher mortality and increased fractures and falls. We definitely do NOT want to be losing muscle mass. This study did not reveal whether the intervention group was sedentary, or exercise let alone engaged in strength training. I would like to see a study done with the participants using a combination of daily 16:8 intermittent fasting earlier in the day, strength training & optimal nutrition to include daily protein intake as interventions. See more on the importance of muscle mass below.

Train fasted & finish eating early

There’s conflicting information in the scientific literature with regards to training fasted. In a systematic review and meta-analysis (see paper HERE) researchers found no changes between fasted and fed conditions pre-aerobic activity for less than <60 minutes, however pre-feeding for greater than >60 minutes showed aerobic performance capacity to improve. This means those engaging in any type of endurance aerobic training beyond 60 minutes would benefit from doing so in a fed condition. There’s less science with regards to strength training and IF, however we do know that whilst we are taxing our muscles in a fasted state we are not storing protein, so it’s a good idea to replenish protein after a workout (a smoothie is easy to get approx. 20-30g protein) whilst our muscles are primed for more protein. This will help to raise IGF-1 (growth pathway) levels and some whole food cellular carbs, which makes IGF-1 more bioavailable. 

Women in particular need to slowly ease into IF

Also, women who dive into IF who are not yet metabolically flexible can be at risk of hormonal imbalance. Most women need to slowly ease themselves into IF and not opt for a shorter eating window, to begin with. Individualization is paramount when it comes to women which is why they shouldn’t be grouped with men as they have in this particular study. I recommend to my clients starting with 12:12 then moving to 14:10 and much later to 16:8 if they aren’t exhibiting adverse changes in their menstrual cycle, sleep, energy levels, and mood. Often women’s hormones can be adversely affected if they jump in too fast. 

The type of IF I recommend

Let me just say that if you have had a bad relationship with food, have previously had an eating disorder, are a teenager, are pregnant, are breastfeeding, are on medication (unless otherwise advised by your physician) intermittent fasting is NOT for you. Ensuring proper nutrition and education on food choices to optimize your health is far more important! 

I prefer to use intermittent fasting as a tool. It is an intervention that is not the be-all and end-all, rather when used in conjunction with other tools/ interventions can be extremely useful depending on your goals. My approach has always been circadian rhythm IF. The science supports this too with consuming your last meal of the day (dinner) as early as possible. For example, I do 16:8 so breakfast for me is around 10 am and I stop eating after dinner at around 6-6:30 pm with the kids. I do not look at IF as a rigid-regimen in which I cannot socially go out and dine until hours later – I enjoy those times too! This mindset creates a bad relationship with food. Most of the time what we do is what matters, so this works for me. I also train fasted in the morning. I do not recommend IF if it means waiting until 2 pm for your first meal of the day. This also requires eating late into the night. Science supports eating earlier in the day when our metabolism is operating at its peak. Eating late into the night I have seen backfire which can lead to binge eating, digestion issues & hunger hormones being out of whack. IF along with exercise helps you to become more metabolically flexible whilst increasing insulin sensitivity.

Here are a few of the doctors who I consider experts on intermittent fasting and who have helped me in my journey and will perhaps in yours too.

  1. Dr. Valter Longo, Professor biogerontologist and cell biologist at UCLA has found tremendous efficacy in his research with IF. In particular on cellular protection, aging, diseases, and longevity along with helping to relieve autoimmune disease symptoms. His website can be found HERE.
  2. Dr. Jason Fung M.D. of The Fasting Method found HERE is a physician, researcher, and author in Toronto helping people reverse type 2 diabetes and metabolic diseases with fasting. I have included a recent CrossFit health webinar YouTube video interview with Dr Fung which is worth watching. In his years of clinical practice, he has experienced significant benefits with his patients using intermittent fasting. Watch HERE.
  3. Dr. Amy Shah, M.D. is an Integrative Medicine Doctor and author with training from Cornell, Columbia and Harvard Universities. She is also known as the fasting MD and I really like her female-centred approach. Fasting for women is not the same as men and if not done correctly can cause a cascade of hormonal imbalances. Her website and fasting protocols can be found HERE.

The importance of muscle mass

Rather than being fixated on losing weight – we need to be focused on BUILDING lean muscle mass. We need to RESIST our muscles. It’s a type of “savings” investment for our future. A contributing factor to morbidity & mortality is ‘falls’ as we age. 

We NEED to be protecting our joint, bone, heart, brain, & metabolic health NOW! Body composition is nice to have bi-product. Our primary concern is to RESIST our muscles to prevent age-related diseases. 

This means resistance training. Weights, lifting, bands, even bodyweight offers muscle resistance. Walking the dog, or to the park, etc isn’t going to cut it. These are nice forms of great steady-state cardio, but you’re NOT resisting your muscles. 

WHY we need to hustle for that lean muscle:

Muscle is our metabolic currency.

It’s our glucose disposal/insulin sensitivity & determines our carbohydrate threshold. 

Muscle affects our brain, bones & immune system. Skeletal muscle is our largest endocrine organ. 

Research shows that gains in muscle mass (hypertrophy) can reverse some of the biomarkers of aging. Consequently, a decrease in muscle mass (we lose up to 10% per decade!) will age us FASTER. 

Aside from mobility, when we contract our muscles interleukin-6 is secreted which helps to augment our immune system & reduce inflammation. Also, exercise-induced myokines have profound effects on both skeletal muscle & our brain. Muscle secretes BDNF to feed our brain. 

Muscles are our largest tanks for glucose disposal (from carbs consumed). Fit peeps are able to consume more carbs because they’re constantly using their muscles. When we contract our muscles we activate a pathway that is independent of insulin to burn even more glucose. The goal here is to become insulin sensitive so that our muscle cells are primed to burn more glucose (sugar) instead of accumulation of adipose tissue (fat.) 

When we push to near failure whilst applying progressive overload we make muscle gains. Muscle protein synthesis (growth) is critical too. High-quality dietary protein along with proper nutrition & sleep is key.

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