Calorie (or dietary) restriction is the most effective intervention for increasing lifespan in laboratory animals. It activates or deactivates a number of physiological pathways, leading to increased stress resistance. In most studies, lifespan extension occurs to the degree of restriction of food: the greater the restriction, the longer the life. (Up to the point of actual starvation.) But a new study has found that only ten percent dietary restriction significantly extends lifespan.
The big drawback with calorie restriction as it concerns humans is that it’s difficult to do. Humans aren’t confined to cages where they can be fed according to a scientist’s schedule.
Humans who undertake calorie restriction (CR) report being cold and lacking energy as well as having a lower libido – and this is *all* the time.
Most people who undertake CR have done so at a level of perhaps 20% fewer calories than a normal person would eat; partly this has been done since it’s been thought that a minimum level of restriction is necessary to see any benefits, and partly because it’s been thought that the more restriction, the greater the benefits. And partly because restricting even more than 20% is very difficult when done over a long period of time.
So a group of researchers wanted to look at lesser levels of CR and see how well they would work: Significant life extension by ten percent dietary restriction.(1) The animals used were rats, and divided into 3 groups: ad lib fed, 10% restricted feeding, and 40% restricted.
The data show that the restriction in calories does not affect lifespan in a linear fashion. It’s more a pattern of decreasing returns as restriction becomes more severe. That’s the biggest takeaway point from this study.
Given my concerns of late, I would have liked to see the researchers measure the iron content of the rats’ bodies, but they did not. I did note that the diet contained “5% Ralston-Purina mineral mix”, but I’ve been unable to find out how much iron this represents.
It’s thought – though most other scientists seem to be ignoring it – that CR results in far less iron accumulation and may be a major reason why CR extends lifespan.
If it’s true that less accumulation of iron is a major cause of the effects of CR, then it follows that you can obtain many or most – or even all – of the benefit just by keeping iron levels low. No pesky calorie restriction needed.
Another application to humans is that 10% CR is not so severe. However, the question that arises in my mind is, 10% compared to what? Calorie intake has increased in the US from about 2100 calories a day in 1970, to about 2500 a day now.
If you cut your calories 10% compared to what everyone else is eating, you don’t even get down to 1970 levels. That’s a 10% cut compared to the average fat, sick person.
Probably to see any benefit, the cut would need to be 10% of what keeps you at a normal weight.
I can’t remember where I got the following quote, but it shows the limitations of CR in humans: less than 3 years of increased life at the cost of decades of severe, 30% CR, with continuous hunger, cold, and low sex drive. No thanks.
But, you could capture most of that benefit by only 10% CR, or so it seems. And in fact, iron restriction is an even better way, with no hunger, cold, or low libido to deal with.
When animals are calorie restricted, they rapidly lose body fat, and this could be another reason for its effect. Fat tissue is a source of inflammatory cytokines, and even a little bit causes insulin resistance to increase. Excess body fat accelerates aging.
The lesson for life extension as it applies to humans is that body fat, like iron, should be kept minimal. Ten percent CR over a long period would certainly do away with excess body fat. A low-carb diet is arguably an easier way to do that, however. Or the use of intermittent fasting.
It’s also been found – or at least thought – that restriction of protein may confer most of the benefits of CR. One could cycle protein to get the benefits while retaining and building muscle. I’ve begun to lower protein intake myself by 1) intermittent fasting and 2) on non-workout days, one of my meals is low-protein.
Calorie restriction does not have to be severe to have a significant and substantial benefit on lifespan.
Keeping iron in the low normal range may give you much of the benefit of CR.
Excess body fat is to be avoided.