Let me start by saying that I’m a fan of intermittent fasting. I think going for extended periods without eating was probably normal for humans throughout most of our evolution, and I’ve seen enough evidence to convince me that it can help with everything from weight loss to improving insulin sensitivity to boosting the immune system.
Martin Berkhan at Leangains and Paul Jaminet at Perfect Health Diet both write extensively about the benefits of intermittent fasting, so I’m not going to cover that here.
Instead, I want to talk briefly about when intermittent fasting might not be a good idea. I haven’t arrived at this notion through combing the research literature, but through direct experience with patients in my clinical practice.
In the last few months I’ve had a few patients come to me with several months of low-carb, paleo nutrition and intermittent fasting experience behind them. When I had them test their blood sugar with a glucometer, we discovered some very erratic patterns. They didn’t just have high fasting blood sugar in the morning, as is typical with low-carb dieters, but they had high levels or a “yo yo” pattern throughout the day.
I tested the cortisol/melatonin rhythm in two of these patients, and it was off in both of them. Why would this be? It’s possible that the blood sugar ups and downs they’re experiencing are exhausting their adrenals. Or, that their adrenals were already under stress and the repeated cortisol secretions necessary to bring their blood sugar back up when it drops created further stress.
As an experiment we decided to have them try eating regular meals, and even more frequently than normal (i.e. every 2-3 hours). Guess what? Their blood sugar normalized within a few days, they started sleeping better and other symptoms improved. I’ve only re-tested cortisol rhythm in one of these patients, but it was back in the normal range after three weeks of eating more regularly.
So how could intermittent fasting normalize blood sugar in some people, but throw it off in others? I’m not sure, but as I said above, my guess is that it has a lot to do with their adrenal status when they begin fasting. There’s a complex relationship between blood sugar and hormones like cortisol, glucagon, epinephrine, norepinephrine and growth hormone. While it’s true that balancing blood sugar can bring the hormones back into line, it’s also true that hormonal imbalances can throw blood sugar out of whack.
I’ve heard anecdotal reports from some that intermittent fasting was rough on them when they first started, but after sticking with it for quite a while it had the desired effect. It’s possible, of course, that if these patients of mine had simply kept going their blood sugar and insulin sensitivity would have normalized. But three of them, at least, had been doing it for six months or longer before they came to me – so I think it’s unlikely that another few months would have made the difference.
As usual, I’d love to hear your thoughts on this.