Hi Karen, Welcome to the CR Forums! Thanks for your questions. I'll try to answer them. Somewhere around 2005 - 2007. There is some discussion of my diet evolution earlier in in this very thread (which I'd forgotten!), but the best discussion of my protein history and motivation for reducing it can be found in the following discussion between Michael and me: The TLDR of the above thread is that back in the early days of the CR Society (early 2000s) both he and I used to eat a relatively high protein diet (~30% of calories - 30/40/30 "Zone Diet") until we participated in a human CR study by Luigi Fontana [1] which found that those of us who were following a high protein CR diet had a relatively high level of IGF-1, which has come to be though of as pretty pro-aging. For a discussion of the tradeoffs associated with high vs. low IGF-1, see this thread: Back to your questions: I've never noticed that protein per se was a big driver of my muscle mass. When I went on CR in 2001, I dropped about 45 lbs (172 -> 127, BMI 25.8 -> 19.0). During that drop I lost quite bit of fat, as well as muscle and bone mass. It's just something I accepted. I've always done a modest amount of weight training, and haven't changed that in an attempt to maintain extra muscle. I consider my muscle mass sufficient for health purposes and enough to avoid late-life sarcopenia.  Because I'm once again exercising an unusually large amount (after a drop for while in 2017), I eat a lot of calories and despite being a vegan, my protein intake is more than adequate - in the neighborhood of 100g / day. I've never worried about it beyond trying to keep my protein intake from being too high (see above threads). If I'm getting enough high-quality calories from a variety of (vegan) sources I figure I'm getting sufficient protein. --Dean ------------ [1] 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.

Author information:
(1)Division of Geriatrics & Nutritional Sciences, Washington University School of
Medicine, St Louis, MO 63110, USA. lfontana@dom.wustl.edu

Comment in
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
dietary interventions.

PMCID: PMC2673798
PMID: 18843793