Intermittent Fasting: The Science & Tradition

Over the years, a lot of people (both students and clients) have asked me about intermittent fasting. They want to know how it works and, more importantly, what they should be doing. Those are actually two completely different questions. I can share with you, based on my understanding of the science, how intermittent fasting works. But I can’t tell people what they should be doing. Each person is too unique, too different, and I have to remain firmly within my scope of practice. I’m not a dietitian, and I don’t know enough about any individual’s health history to give personalised prescriptions. I can only share the science, even the yogic tradition, and what I do personally, in the hope that it might get you to think a bit more deeply. But anything like this, especially if you have existing health issues, should be discussed with a qualified medical professional or dietitian rather than a yoga teacher.

That said, I am going to share with you some of the science, explained really simplistically so you can understand why intermittent fasting can be so effective.

We use glucose every day for energy ⚡️. Glucose is created from the food we eat and becomes our primary source of fuel ⛽️. It’s stored in the liver . When you fast, you essentially go into a form of starvation mode. Your brain 🧠 starts to convert fatty acids into energy in the form of ketones. Pound for pound, ketones give you more bang for your buck.

An quick analogy that might help -

Glucose is like a small, quick-access petrol tank. It powers the engine (our brain 🧠) immediately after you eat a meal. This fuel is convenient and fast-burning, but the tank is limited in size (your liver and muscles can only store so much glycogen).

Ketones, on the other hand, are like switching over to the large, long-range diesel reserve or the highly efficient alternative fuel system. When glucose levels drop, our liver starts converting stored fat into ketones. These molecules serve as a cleaner, more energy-dense fuel source. Pound for pound, they deliver more sustained power with less waste, allowing the engine (especially the brain) to operate smoothly for extended periods without performance drop-off.

This is completely based on our ancestry: our ancestors could go days without food. They would binge when food was available and then go long stretches without eating anything. But the brain still needed to survive, to perform, and the body still needed to remain relatively strong so you could hunt or gather the next meal. And so we shift into this ketone state where the brain uses fatty acids for energy rather than glucose - which is far more productive. You might find that cognitively and physically, after a fast, you still feel surprisingly good.

Personally, I always train in the mornings (whether it’s lifting weights or yoga, whatever the physical activity). I prefer to train fasted. Anytime there is a physical demand on me, the emptier my stomach, the better I am. I don't have a pre-workout meal. I would last 5 minutes 🤮

And if there’s a cognitive demand on me 🧠, say I’m yoga teacher training all morning - where I’m talking theory, science and tradition, I stay fasted because I feel much more alert and aware 🤔. I would never have breakfast; that would spike my insulin and leave me feeling lethargic for hours. So for those of you that have studied with me, be it teacher training, Yin TT, or Back pain, where I am talking my talk blurting out the science all day - its always 100% fasted. Driven by coffee ☕️

That’s the kind of basic, simplified science behind how it works.

In terms of recommendations, the science varies on what most people “should” do. I personally am not religious with my fasting, the same way I’m not religious with my training. It’s just something I do without obsessing over it. I tend to sleep all night without food (like most of us), and I tend not to eat in the morning. I usually eat around lunchtime, midday or one o’clock, making sure what I eat is quite rich in protein because my body needs that resource after the night of “starvation.”

That’s my usual protocol. Sometimes if I’m busy with clients I might not eat until three, and then my feeding window runs from three until ten PM - and trust me, I pack in the calories during that time 🫣. But I tend not to eat when there’s a big cognitive demand on my brain. I trust the process, I trust the science, and it really does work for me.

As far as the yoga tradition goes, I wanted to look beyond modern Western opinions and go straight to the classical sources from the subcontinent - texts written by Indian yogis and sages centuries ago.

The classical hatha yoga texts place a strong emphasis on mitāhāra - moderate, measured eating - rather than extreme or prolonged fasting. In the Hatha Yoga Pradipika (1.58), it is said: “A moderate diet means eating satisfying, sweet food for Shiva’s pleasure, while leaving the stomach one-quarter empty.” The Gheranda Samhita (5.22) is even more specific: “Half the stomach should be filled with food, one quarter with water, and one quarter should be kept empty for practising prāṇāyāma.” This measured approach balances the elements in the body (earth, water, fire, air and space) and leaves room for the breath and digestive fire to work efficiently during practice. The texts repeatedly stress that yoga is not achieved by extremes - neither by overeating nor by excessive denial. The Gheranda Samhita (around verse 30) explicitly cautions against eating only once a day or doing too much fasting, while the Bhagavad Gita (6.16) reminds us: “Yoga is not possible for him who eats too much, nor for him who does not eat at all.” The Hatha Yoga Pradipika even lists fasting among the external acts that, on their own, do not bring about the experience of yoga.

At the same time, the broader yogic and Ayurvedic tradition (which has always been intertwined with yoga) views upavāsa (fasting) not merely as calorie restriction but as a sacred practice of “staying near” the Lord (upa = near, vās = to stay). It is understood as a form of purification that helps remove āma (undigested toxins), lightens the body, sharpens the mind, and creates the inner space needed for meditation and self-inquiry. In this traditional view, periodic fasting supports sattvic clarity, strengthens willpower, and aligns the physical and subtle bodies with cosmic rhythms. It is seen as one of the supportive disciplines (sometimes described in broader yogic literature as part of the observances or tapas) that aid the practitioner on the path, provided it is done with intelligence and not to the point of weakening the body needed for sustained sadhana.

So the classical tradition doesn’t prescribe a rigid intermittent-fasting schedule like we see today. Instead, it teaches balance: eat with awareness, in moderation, and use periods of restraint wisely to support your practice rather than undermine it.

That’s what I’ve taken from the texts and from my own experience. I hope this gives you some food for thought (literally and figuratively).

Ultimately, intermittent fasting is not a magic solution or the latest wellness trend. It is simply one practical tool that can support energy, focus, and resilience when used intelligently. The science explains why it works; the tradition reminds us to avoid extremes. I share my own approach not as a prescription, but as one example of what works for me and how the balance of science and tradition is found. Listen to your body, respect your limits, and make informed choices with the right professionals. That measured approach has served both my practice and my teaching for years.

If you have any questions, let me know. Email back or chat to me at the studio as there are so many nuances to all of this I wouldn't know where to start. And finally, don't just do what people recommend on podcasts. Do you own research first as there is ALWAYS alternative perspectives that might work better for you.

Namaskar

Zahir

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