Did you know there are more books published about fasting diets than there are clinical research papers?! Ultimately, my question for you is - what are you hoping to achieve by fasting? Fasting is a strategy.
Let's define fasting.
What is a Severe Fast?
Caloric intake is at 70% Energy Restriction. Based on an average 2000cal daily adult diet, this equates to 600 calories on fasting days e.g. OPTIFAST diet or VLCD
What is a Moderate Fast?
Caloric intake is at a 30% Energy Restriction and the diet is based on the AGTHE. Based of average adult 1,400Cal/day. Most people will achieve this and lose weight when they follow the AGTHE for their age and gender! WITHOUT 'pop diet culture fasting'!
There are different types of fasting trends in popular diet culture:
1) Time Restricted Fasting (TRF) e.g. The 16 hour fast (aka Intermittent fasting)
2) Alternate Day Fasting (ADF) whereby 75% Energy Restriction occurs on Fasting days alternating with Feed Days (total energy requirements met)
3) The 5:2 diet - fast for 2 consecutive or non-consecutive days in the week (~500calories on fasting days) and eat total energy requirements on remaining 5 days
4) Warrior Diet - fast during the day and have only 1 meal at night
5) Eat Stop Eat - Fast for 24 hours 1-2 days in the week
So, what is the truth? Will fasting help you lose weight and improve your health biomarkers? For a diet to lead to weight loss, calories burned must exceed calories consumed to produce a calorie deficit. Intermittent fasting diets assume that the large calorie deficit produced by fasting is not recovered during the unrestricted period, so the calorie deficit is preserved. However, eating a little more and reducing spontaneous physical activity may be enough to recover the calorie deficit.
A study showed that skipping breakfast for 6 weeks reduced physical activity and increased calorie intake at later meals. This was enough to fully compensate for calories skipped at breakfast. This raises the question: Is fasting or severe calorie restriction worth the effort? Bottom line: Compliance and Consistency is key for the success of any diet.
In terms of biomarkers - research has shown:
- Intermittent Fasting and Continuous Energy Restriction resulted in similar weight loss and improvements in Cardiovascular risk factors after 12 months (Sundfor Nutr Metab Cardiovasc 2018, Conley Nutr Diet 2018)
- The 5:2 diet is as effective as Continuous Energy Restriction (CER) in weight loss, insulin sensitivity and health biomarkers (Harvie IJO 2011, Antoni British J nutr 2018)
- IER is an effective alternative diet strategy for the reduction of HbA1c and is comparable with CER in adults with T2DM (if individuals with T2DM are going to be fasting, they NEED TO adjust their medication protocol to avoid hypoglycaemia!)
- Alternate day fasting was not superior to the Continuous Energy Restriction when comparing cardioprotection biomarkers (blood pressure, heart rate, trigs, fasting glucose, fasting insulin, insulin resistance, CRP) (Trepanowski J, JAMA 2017)
So, what are your goals? What do you hope to achieve following this plan? How is this plan going so far? What do you like about the plan? Is this strategy for you? You wont know until you've trialed, maybe failed and corrected the strategy.
In a recent ABC catalyst documentary @drjoannamcmillan worked with a team of researchers to get down to “The Truth About Fasting”. Some take home messages I heard were:
They are still researching to answer questions about the best fasting regime!
What works for one person may not work for another. The science is still emerging about fasting
One could argue the benefits participants experienced was because of the change in their food choices, not the fasting
It was concerning that some participants lost lean muscle mass!!! Which drives metabolism faster
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