Fasting vs Calorie Restriction with Exercise

Published 9.1.2012, updated 9.5.2012; reformatted 4.6.2013; and again 9.22.2015
To be clear, the topic here is long term severe calorie restriction. People following this concept deliberately eat 25% fewer calories than required to maintain a normal weight. It is sometimes called CRON, which stands for calorie restriction optimal nutrition. The idea being that if you're going to eat a minimal number of calories, all of those calories have to be nutritionally dense. The thinking is that consuming fewer calories will extend lifespan.

The inspiration for this article was the recent BBC Horizon program with host Michael Mosley. Entitled Eat, Fast and live longer, the program follows Mosley as he learns about research to extent lifespan using calorie restriction techniques.

It's an interesting program, well worth a watch. In the end, Mosley decides that an eating regime in which he "fasts" two days a week, then eats without restriction the other five days is the best choice for him. The word fast about is in quotations because he doesn't actually go without eating. Instead, on "fast" days he eats only 600 calories, which is not that much food.

Full fasting proves too difficult for him, especially as he decides to do it for 3.5 days. In that personal experiment, he drank water, black tea and 50 calories of soup each day. He's also uninterested in simply restricting calories. The show begins with his visiting a man about his age (in his 50s) who eats about 1900 calories a day. Mosley claims to eat about 2300. The guy who eats 1900 only weighs 134 pounds, but his health markers are those of a much younger person. I would point out that both those totals are less than the estimated typical intake for American males.

Mosley also wrote an article for the Telegraph about his exploration. It's a good outline of the show, if you don't want to watch a 55 minute video.

Not a Panacea and with Potential Unintended Effects

Coincidentally, calorie restriction and whether it extends lifespan is in the news again, here's the NY Times reporting. New study results indicate that severe (defined as 25% or greater) restriction of daily intake below that required to maintain a normal weight did not increase the lifespan of monkeys. Here is Marion Nestle's take and here is Stephan Guyenet's. Neither is surprised at the findings; and neither is a fan of calorie restriction. Nestle points readers to this JAMA article that found that the lifespan vs BMI curve (BMI along the x-axis) is U shaped. In other words, you die sooner if you are too far or too thin. As an aside, many medical curves have U shapes, including blood pressure and cholesterol. Too low can be as dangerous as too high.

Ray Kurzweil is a fan of CR (calorie restriction), as described here, however, he suggests a less severe restriction of 15% of optimal weight calories. He also says to make the minimum weight 95% of your "optimal" weight. So what is optimal weight for a CRON follower? A BMI of 18.5 or 25, which are the extremes of the "normal" weight range? Below a BMI of 18.5 the death rate is higher in the lifespan vs BMI curve.

I do not fast intentionally, meaning that I don't designate any particular day one during which I will not eat my usual amount of food. Fasting holds no interest for me because it is unpleasant to be hungry and not eat. No part of my life plan includes avoidable suffering. That said, if I'm not hungry, I don't force myself to eat, which occasionally results in my eating a much lower calorie total. Those days are rare, and typically involve some sort of travel.

Here is Slate's coverage of the monkey trial. It makes a good point, in that perhaps the amount of what you eat isn't what's most important, eating well (nutrient dense foods) is what makes the largest difference. So perhaps by limiting your intake (because eating healthily will lead to eating fewer calories overall) you will have a healthier existence, but not necessarily longer.

CREX

Exercise was not considered in the BBC program, in fact, the host was keen to avoid most anything that would involve doing extra activity. He wanted to change to his his life as little as possible. But I not only have trimmed my portion size, I have increased the amount a move during the day with my treadmill desk.

To some extent, I use the calories expended while walking and typing as a way to relax the need for stricter portion control. In other words, I eat (and drink) some of those calories that I use while walking up to 10 miles a day (which represents a five hour work day at two mph). So does the fact that my walking creates a significant calorie deficit create a "severe" calorie restriction for me? This is the concern that prompted these musings.

And exercise has been shown to have a similar effect as CR— in other words, if you expend more energy and continue to eat the same amount, it's the same or better than if you had cut calories. It doesn't get as much attention, because most people are sedentary. So when weight loss in considered, mostly we're talking eating less. There was no difference after 6 months between subjects who restricted calories by 25% and subjects who restricted by half that amount, but exercised to make the total calorie deficit 25%.

All of this makes sense in terms of the energy balance of course, but frankly I think (I know) that I would rather move a bit more so that I could eat more.

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