Hi,
It’s Dee here 
In this week’s edition of Health in 60 Seconds:
Fasting has been a big trend the past few years – but the benefits of fasting depend on how long you fast – and who you are
Plus: why persistent tiredness isn’t always just “normal life” catching up with you – and the simple tests we often recommend to help get to the root of it.
Let’s dive in 
1. Research Corner
Fasting Length vs. Benefit: What the Research Shows
Intermittent fasting has become one of the biggest wellness trends of the past decade – but not all fasting windows offer the same benefits.
Here’s what the research shows:
12-hour fast (e.g. 7pm–7am)
Supports metabolism, liver health, and circadian rhythm May improve blood sugar and insulin resistance when paired with a healthy diet
A gentle, sustainable starting point – likely the minimum fasting length to see benefits
16-hour fast (e.g. 16:8 method) Linked to fat loss, improved insulin sensitivity, and reduced inflammation
May initiate DNA repair and autophagy
May enhance mood, antioxidant capacity, and eating behaviour Nutrient density becomes more important with a shortened eating window. At Coho we’d usually advise on 14 or 16 hours, if we felt it was right for you – for example, stress, mood, energy and hormones are super important considerations
24-hour fast (1–2x/week) Supports autophagy, insulin regulation, and cardiovascular markers May improve arterial stiffness and reduce inflammatory metabolites Not suitable for everyone – especially those with hormone, energy, or blood sugar challenges
72-hour fast (used occasionally) May support immune reset, lower blood pressure, a more profoundketosis and autophagy
Should be done with guidance – long fasts carry risks for many people
Bottom line: Fasting can be powerful – but the right approach depends on your health status, goals, and what your body actually needs.
This Isn’t “Just Normal Tiredness”
Struggling with brain fog, energy crashes, or waking up just as exhausted as when you went to bed?
This isn’t “normal tiredness” – even though busy lives can make it easy to keep pushing through.
These are red flags we often see in clients with hidden post-viral fatigue, mitochondrial issues, chronic fatigue syndrome or Long COVID.
If your body isn’t bouncing back – no matter how much rest you get – there’s likely a root cause worth exploring.
We break it down in this Instagram post →
Bonus info
And if you’re feeling constantly tired, these are some of the routine blood tests we recommend starting with – plus the Coho optimal ranges we aim for:
-
Ferritin (iron storage)
▸ Optimal: 50–90 for women, 50–300 for men
▸ Anything under 50 may affect energy and mood -
Haemoglobin
▸ Optimal: Over 132 g/L -
Vitamin D
▸ Optimal: 100–150 nmol/L
▸ Never go over 200 nmol/L
▸ Most lab reference ranges start at 50 nmol/L, which is too low for optimal health
-
Serum B12
▸ Optimal: Over 350 ng/L -
Serum Folate
▸ Optimal: Over 14 ng/mL
Testing is a powerful first step in understanding why you’re tired – so you can move beyond symptoms and start rebuilding energy the right way. We perform more in-depth testing in chronic tiredness too, for instance by looking at viral load, but the above is a good place to start.
Health in 60 seconds, as promised…
Dee Brereton-Patel
Founder, Coho Health
