Most of the recent documentaries and newspaper pieces on calorie restriction haven't really offered anything new. They pretty much just repeat the same old arguments about mice eating less and living longer, and then joke that starving yourself will at least make your life seem longer.
This recent BBC Horizon documentary was a positive surprise, however. It does a pretty good job of covering both traditional calorie restriction (CR) and various forms of intermittent fasting (IF), and while the scientists are overly optimistic about either strategy extending maximum lifespan in humans, they do make some good points.
There's for example Luigi Fontana, something of a celebrity in the CR research field, who thinks practicioners of calorie restriction are so much healthier than the average person that they almost "belong to another species". Right. The host of the show correctly points out that Joseph Cordell, the decade-long CR practitioner he interviews, doesn't look remarkably younger than the average 50-year-old.
His blood tests do indicate a very good health, however, and what's interesting is that Cordell is not severely calorie-restricted – he eats 1,900 kcal per day. For an average male, I think that's entirely doable, as long as you pay attention to the nutritional value of the diet to avoid hunger. Cordell also doesn't have that "cancer patient" look to him that a lot of CR skeptics worry about; he's thin but not overly so.
Several of the scientists and professors in the documentary seem to think that intermittent fasting is as good as calorie restriction for longevity, even though the evidence shows otherwise: in animals, IF results in increased lifespan only to the degree that it also results in CR. One of the researchers advocates a diet of fasting and feasting every other day, but not in the traditional 24-hour cycles. Instead, she recommends eating around 400-600 kcal on the fast days and as much as you like on the feast days.
In my experience, at least the 24-hour cycle of fasting and feasting (where you're not allowed any calories during the fast) results in eating twice as much during feast days, unless you purposefully count and restrict calories during feast days as well. She says that there is a calorie deficit, however: during fast days, you're allowed around 25% of your normal calorie intake, and during feasting days you naturally end up eating around 110% of your normal intake. This sounds very strange to me, as it would mean an easy way of accomplishing rather severe CR. I am intrigued by this semi-fasting approach, though.
Another form of IF tried in the documentary is alternate-day feeding based on weekdays instead of 24-hour cycles, i.e. you eat on Monday and then don't eat on Tuesday etc. This is much more difficult than IF based on a 24-hour cycle, since you're essentially fasting around 32 hours at a time. Then there's the 5/2 approach, where you eat for 5 days and then fast for 2 days. And the "4 days of fasting every few months" approach. In the IF circles, there's still debate over which approach is best. Last time I looked, nobody knew the answer to how many hours of fasting is needed to produce the best benefits in humans.
A point that keeps coming up in the documentary is the effect of IGF-1 on aging and the effect of fasting and/or calorie restriction on IGF-1. As Fontana's research suggests, lowering IGF-1 may be crucial for any lifespan extension effects of CR. The 4-day fast clearly lowers IGF-1, but the effect doesn't last long. Cordell's IGF-1 levels are not shown, but since his blood parameters are those of a young man, I assume his IGF-1 is lower than average; probably due to a combination of slight CR and protein restriction.
If you ignore the unrealistic expectations of extending maximum lifespan in humans, the results are overall pretty optimistic. It seems that even a slight reduction in calories and fasting every now and then might significantly improve your health parameters.
Put another way, IF and CR might not make humans live to 120, but they might make you live to 100 without dying of the usual killers like cancer and heart disease. I haven't heard of Joseph Cordell before and am not familiar with how all of his biomarkers look like, but if it is true that he eats 1,900 kcal per day and has only been doing CR since his 40's, perhaps I've underestimated some of the potential benefits of eating only slightly less. Personally, I haven't been doing intermittent fasting for a couple of years now, but I guess it's time to read up on the latest studies and see what's happening out there.
For more information on calorie restriction and intermittent fasting, see these posts:
Antioxidants and Intermittent Fasting – Good For Longevity?
How to Deal With the 5 Most Common Difficulties of Fasting
Alternate-Day Feeding and Weight Loss: Is It the Calories Or the Fasting?
Anti-Aging in the Media: New York Times on Caloric Restriction and Resveratrol