Wednesday, January 28, 2009

Calorie Restriction and Memory - Low-Carb wins again, actually...

This study is the latest to make headlines around the world as it is claimed that modest calorie restriction in elderly people can result in an improvement in memory. From the abstract:
Animal studies suggest that diets low in calories and rich in unsaturated fatty acids (UFA) are beneficial for cognitive function in age. Here, we tested in a prospective interventional design whether the same effects can be induced in humans. ......We found a significant increase in verbal memory scores after caloric restriction .... which was correlated with decreases in fasting plasma levels of insulin....No significant memory changes were observed in the other 2 groups. This interventional trial demonstrates beneficial effects of caloric restriction on memory performance in healthy elderly subjects.
However, what caught my eye in reports of the study was this:
However, care was taken to make sure that the volunteers, despite eating a restricted diet in terms of calories, carried on eating the right amount of vitamins and other nutrients.

Now, this is an important point - it was even - implicitly - used as an objection to the approach by an anonymous dietician who said that:

....people, particularly those already at normal or low weight, should be "extremely careful" about attempting such a diet. She said: "There is otherLink evidence that, far from enhancing memory, dieting or removing meals can interfere with memory and brain function.
presumably because it follows that if you just cut calories by 30% you cut nutrition by 30%.

But these people claim they didn't reduce the subjects intake of vital nutrients, how did they manage this?

The truth is revealed in the (rather limited) data in the Table S2 in the supplementary information package.

For individuals in the caloric restriction experimental group the mean calories fell from 1843 to 1630, the mean protein intake went from 77g to 71g (all numbers rounded to nearest whole number), the mean fat intake from 70g to 57g and the mean carbohydrate intake from 192g to 74g!! Converted to percent energy measures, this means the mean values went from 17% protein, 35% fat and 43% carbohydrate to 24% protein, 43% fat and 25% carbohydrate (the values don't add to 100% because alcohol intake was included). In other words caloric restriction was achieved, without compromising nutrition, by restricting carbohydrates (especially one imagines typical nutritionally empty carbohydrates like products made mainly of white flour and white sugar).

Interestingly, the individuals in the second experimental group which increased its unsaturated fat intake (to 68% of total fat intake on average - that's 36% mono-unsaturated fat which didn't actually increase (baseline for that group was 36%) and 32% polyunsaturates (from 15%)) didn't show the memory improvement, although they also appeared to have achieved a conversion to 'low-carb'. However, in their case the standard deviation for carbohydrate intake was bigger than the mean value (and much larger than the baseline value), which suggests a huge variation within the group.

Another caveat is that while taking the mean values of consumption and converting to calories reproduces (to within 40 calories or better) the reported mean caloric intake for the before case in all the groups, it is does not do so for the after case (the discrepancy is as much as 400 calories - and in all cases the mean nutrient data (in grams) result in an under-estimate of the mean calories). A better model - using a normal distribution for each parameter - might give an idea as to why this is so. Another interesting fact related to this is that - apart from the unsaturated to saturated fat ratio for the unsaturated fatty acid experimental group, none of the reported differences in before and after macronutrient mean intakes were reported as significant.

To sum up: the calorie restriction appears to have been mainly achieved by restricting carbohydrates. The researchers claimed that they had achieved calorie restriction without reducing nutrient content of the diet. The only way to do this is by removing or significantly reducing nutritionally empty carbs e.g. see here. Mean dietary data reported from the study lends support to this theory. The results observed in the subjects e.g. reduced insulin levels also support this theory.

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