Dr. Greger has authored an article today for the very popular health & wellness website Care2 titled How Does Obesity Increases Cancer Risk?
The interesting part is that he focuses on the cancer promoting effects of IGF-1, and uses data from Luigi Fontana's studies (particularly ) of some of us long-term CR practitioners. He also mentions the CR Society by name in the article! Unfortunately, he doesn't include a link to the CR Society website , but I've included one in the comments.
Here are the relevant passages:
The only dietary group that comes close to the recommended BMI of 21 to 23 were those eating strictly plant-based diets, so maybe it’s the weight loss that did it [i.e. reduced IGF-1 - DP].
To put that to the test, we’d have to find a group of people that eat meat, but are still as slim as vegans. And that’s what researchers did—long-distance endurance runners, running an average of 48 miles a week for 21 years were as slim as vegans. If we run 50,000 miles we too can maintain a BMI of even a raw vegan. So what did they find?
If we look at blood concentrations of cancer risk factors among the groups of study subjects, we see that only the vegans had significantly lower levels of IGF-1. That makes sense given the role animal protein plays in boosting IGF-1 levels.
But the vegan group didn’t just eat less animal protein, they ate fewer calories. And in rodents at least, caloric restriction alone reduces IGF-1 levels. So maybe low IGF-1 among vegans isn’t due to their slim figures, but maybe the drop in IGF-1 in vegans is effectively due to their unintentional calorie restriction? So we’d have to compare vegans to people practicing severe calorie restriction.
To do this, the researchers recruited vegans from the St. Louis Vegetarian Society, and went to the Calorie Restriction Society to find folks practicing severe caloric restriction. What did they find?
Only the vegan group got a significant drop in IGF-1. These findings demonstrate that, unlike in rodents, long-term severe caloric restriction in humans does not reduce the level of this cancer-promoting hormone. It’s not how many calories we eat, but the protein intake that may be the key determinant of circulating IGF-1 levels in humans, and so reduced protein intake may become an important component of anti-cancer and anti-aging dietary interventions.
The discussion of vegans having low IGF-1, but not the omnivorous (or at least high protein) CR practitioners, comes from the Fontana study , which we've discussed many times before.
What's nice to see is that (for once) Dr. Greger doesn't (directly) promote a plant-based diets in his final analysis. Instead he focuses on the importance of keeping protein intake low as a potential key for preventing cancer. What he doesn't mention is that in , when the CR practitioners reduced protein from 1.67 g/kg body weight to 0.95 g/kg body weight, their IGF-1 level dropped a lot.
This is one of the main reasons that many of us changed from a relatively high protein CR diet that we practiced in the early 2000s to the relatively low protein CR diet that we practice today, and why (I presume) Michael Rae modified the Megamuffin 2.0 recipe, with 28% of calories from protein to the Megamuffin 3.0 recipe, with only 15% of calories from protein.
 Aging Cell. 2008 Oct;7(5):681-7.
Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3
concentration in humans.
Fontana L(1), Weiss EP, Villareal DT, Klein S, Holloszy JO.
(1)Division of Geriatrics & Nutritional Sciences, Washington University School of
Medicine, St Louis, MO 63110, USA. email@example.com
Aging Cell. 2009 Apr;8(2):214; author reply 215.
Reduced function mutations in the insulin/IGF-I signaling pathway increase
maximal lifespan and health span in many species. Calorie restriction (CR)
decreases serum IGF-1 concentration by ~40%, protects against cancer and slows
aging in rodents. However, the long-term effects of CR with adequate nutrition on
circulating IGF-1 levels in humans are unknown. Here we report data from two
long-term CR studies (1 and 6 years) showing that severe CR without malnutrition
did not change IGF-1 and IGF-1 : IGFBP-3 ratio levels in humans. In contrast,
total and free IGF-1 concentrations were significantly lower in moderately
protein-restricted individuals. Reducing protein intake from an average of 1.67 g
kg(-1) of body weight per day to 0.95 g kg(-1) of body weight per day for 3 weeks
in six volunteers practicing CR resulted in a reduction in serum IGF-1 from 194
ng mL(-1) to 152 ng mL(-1). These findings demonstrate that, unlike in rodents,
long-term severe CR does not reduce serum IGF-1 concentration and IGF-1 : IGFBP-3
ratio in humans. In addition, our data provide evidence that protein intake is a
key determinant of circulating IGF-1 levels in humans, and suggest that reduced
protein intake may become an important component of anticancer and anti-aging