Fuel for the carb-protein wars!

[DSeid]

Be warned: these studies will start getting cited in the nutrition wars. Okay that’s the this side of the wall summary of the summary of the studies in last week’s Science. From their other side of the wall synopsis:

Two studies out this week, one in mice and another primarily in people, suggest that eating relatively little protein and lots of carbohydrates—the opposite of what’s urged by many human diet plans, including the popular Atkins Diet—extends life and fortifies health …

… The interplay between diet and health is extraordinarily complicated, and protein diets in particular have sparked confusion. On the one hand, some researchers have found a correlation between consuming lots of protein and heart disease. On the other, high-protein diets have been linked to improved metabolic profiles, such as lower blood glucose levels. Teasing out the role of protein versus total calories or carbohydrates is no easy task. “There are a whole lot of variables here,” says Cynthia Kenyon, who studies the biology of aging at the University of California, San Francisco.

An Australian group led by nutritional physiologist Stephen Simpson and biogerontologist David Le Couteur at the University of Sydney tried to clear up some of the confusion by assigning 858 mice to one of 25 diets with different mixes of protein, carbs, fats, and fiber. All were allowed to eat as much as they wanted.

The mice whose diets included 5% to 15% protein and 40% to 60% carbohydrates lived the longest, up to 150 weeks compared with 100 weeks for those on a diet of about 50% protein. By comparison, Americans on average take in about 16% of their calories from protein. The animals on the low-protein/high-carb plan also had lower blood pressure, better glucose tolerance, and healthier cholesterol. (Levels of fat in their diet didn’t seem to make much difference.)

Mice that ate lots of protein were skinnier—just as people on high-protein diets tend to be. But for these mice, slender translated to ill health and earlier death. This finding, Le Couteur says, supports the “concept of healthy obesity,” which has been raised by epidemiology studies of slightly overweight people. He suggests that if their diet is higher in carbohydrates and lower in protein than usual, that might be responsible.

The second study, led by gerontology researcher Valter Longo and graduate student Morgan Levine at the University of Southern California in Los Angeles, focused on data from 6381 adults over 50 years old who were interviewed once about their diet as part of NHANES, a national survey of health and nutrition. Longo’s team used death records to conclude that those under 65 whose self-reported diets they classified as high-protein—the participants said at least 20% of their calories came from protein—were at much higher risk of illness and death than a group who took in 10% or fewer of their calories from protein. The high-protein eaters were more than four times as likely to die from cancer over the 18 years after they were surveyed, and 75% more likely to die of any cause. …

The actual mouse study.

Th actual human study.

The mouse study in my mind is pretty poor. Studying protein levels up to 60% of caloric intake?? That is more than most think of as high protein. Typical American gets, as noted, about 16% of calories from protein. For most high protein means 25 to 30%. The supplemental information pg 8 gives the actual mortality numbers for the different diet plans. The highest median lifespan was actually a 42% protein diet and it was not far off from the top numbers for longest lifespan. On page 7 of that supplement it is noted that the animals in 3 the low protein groups wer dropped from analysis early because they were too unhealthy (lost too much weight or develped other health issues) to continue. Not quite a fair analysis.

The human study seems a bit better. From its summary:

… Respondents aged 50–65 reporting high protein intake had a 75% increase in overall mortality and a 4-fold increase in cancer death risk during the following 18 years. These associations were either abolished or attenuated if the proteins were plant derived. Conversely, high protein intake was associated with reduced cancer and overall mortality in respondents over 65, but a 5-fold increase in diabetes mortality across all ages. Mouse studies confirmed the effect of high protein intake and GHR-IGF-1 signaling on the incidence and progression of breast and melanoma tumors, but also the detrimental effects of a low protein diet in the very old. These results suggest that low protein intake during middle age followed by moderate to high protein consumption in old adults may optimize healthspan and longevity. …

… The percent of calorie intake from protein was used to categorize subjects into a high protein group (20% or more of calories from proteins), a moderate protein group (10%–19% of calories from proteins), and a low protein group (less than 10% of calories from proteins) …

… Among subjects with no diabetes at baseline, those in the high protein group had a 73-fold increase in risk (HR: 73.52; 95% CI: 4.47–1,209.70), while those in the moderate protein category had an almost 23-fold increase in the risk of diabetes mortality (HR: 22.93; 95% CI: 1.31–400.70). We underline that our hazard ratios and confidence intervals may be inflated due to our sample size and the extremely low incidence of diabetes mortality in the low protein group. Overall, there were only 21 diabetes deaths among persons without diabetes at baseline, only 1 of which was from the low protein group. Nevertheless, despite the small sample size, our results still show significant associations between increased protein intake and diabetes-related mortality. …

… Notably, our results showed that the amount of proteins derived from animal sources accounted for a significant proportion of the association between overall protein intake and all-cause and cancer mortality. These results are in agreement with recent findings on the association between red meat consumption and death from all-cause and cancer (Fung et al., 2010,Pan et al., 2012). Previous studies in the U.S. have found that a low carbohydrate diet is associated with an increase in overall mortality and showed that when such a diet is from animal-based products, the risk of overall as well as cancer mortality is increased even further (Fung et al., 2010,Lagiou et al., 2007). Our study indicates that high levels of animal proteins, promoting increases in IGF-1 and possibly insulin, is one of the major promoters of mortality for people age 50–65 in the 18 years following the survey assessing protein intake. …

This is not enough yet to convince me honestly and for my own sake I am planning to keep up with my relatively high protein high fiber (heavy on the plant derived proteins) nutrition approach. (Not low carb mind you.)

But I am sure that these studies will get cited in the nutrition wars and felt that those who are combatants should get a heads up!

Enjoy.

[Sattua]

Hmm. I don’t have any studies to cite, but hey, we aren’t in GQ or GD here. Here’s my guess:

There’s a segment of the population who run well on a high-carb, low-protein diet, and they happen to also have a much lower risk of diabetes precisely because their bodies handle carbs so well.

Then there’s another segment of the population (of which I am one) whose bodies can’t handle carbs and who become insulin-resistant early in life. This segment finds, consciously or unconsciously, that it feels better on a higher protein diet. Unfortunately our bodies are so whacked that we tend to come down with diabetes and obesity-related diseases much more frequently than the people in the other group.

[SpoilerVirgin]

For anyone interested in this topic, The Hundered Year Diet is a fascinating history of how thinking about the best approach to diet has see-sawed back and forth over the past 100 years.

[DSeid]

Digging more into the article I am less impressed with the second one as well.

Not even any real attempt to control for confounders.

[astro]

Just as a layman there’s also (IMO) a significant difference in people who get lots of protein by being big consumers of fatty meats in fast food (especially beef and pork) and other sources and those who have a higher protein ratio diet with the protein being mostly lean meats and other low fat protein sources.

Plus if following a high protein diet is keeping 20-50 lbs off you would have with a more carb centric diet I would think the overall health benefits of being less heavy would swap the protein risk issues in importance.

[DSeid]

Your first point and Sattua’s are both wondering about confounders - some tendency of those who will later develop diabetes to be in the higher protein group even if they do not have diabetes at baseline just based on who knows how they feel when they eat lots of carbs, what other specifics travel with being in those groups, amount and type of fat, fiber, what sort of carbs … ? And very valid comments I think.

The second point though is exactly the point they are claiming is not true. Thinner with higher protein, in particular animal protein, and lower carb, they claimed, was not healthier in terms of the outcomes measured in the 50 to 65 year old group.

I particular though get cracked up by the fact that they, like the low carb zealots, see insulin as a likely culprit … “Our study indicates that high levels of animal proteins, promoting increases in IGF-1 and possibly insulin, is one of the major promoters of mortality for people age 50–65 in the 18 years following the survey …”

Poor insulin. It gets no respect.

Even more odd to my read is their raising mTOR and IGF-1 as potential evils. The IGF-1/mTOR pathway is requisite for building muscle and mTOR in particular increases with exercise, which obviously is well associated with improved outcomes.