Wednesday, March 19, 2014

Fatness and health among diabetics

The interpretation of weight among diabetics is greatly distorted by the "war" on obesity.  Because diabetes is a nasty condition, researchers are determined to find that obesity causes diabetes, whereas the evidence is at least as good the other way around:  Diabetes causes obesity.  That most fatties don't have diabetes should be sufficient to ignite skepticism in the matter.

The fact that diet can control diabetes does not show that gluttonly causes diabetes.  Just because I put bandaids on scratches, does that mean that bandaids cause scratches?

So I can't see that a population of diabetics tells us much about non-diabetics.  Diabetics are sui generis.

So the study below is not of general interest but is of course interesting to those concerned about diabetes.  There is a popular article here for those who find the journal abstract heavy going.

The results are not nearly as clearcut as some would have it.  The authors are to be praised for the attention they have paid to confounders but that attempt has not clarified the findings.  The difference between smokers and non-smokers is clearly important but the difference in outcome for the two groups is sufficient to be puzzling.  Why do the two groups differ so much? Any answer to that would be speculative so I am inclined to focus on the non-smokers only.  That at least removes an important confounder  -- though the possibility that non-smokers are in important ways more robust from the beginning cannot be excluded.

And the relationship we see there is only weakly linear.  Lifespans for the first four caegories of weight are essentially identical.  It is only among the two fattest categories that there is some elevation of risk.  And, for what it is worth, the skinniest category did have some (slight) elevation of risk  -- echoing findings among non-diabetics.

But in any case no causal inferences should be drawn from this correlational study.  It could be, for instance, that the fatties who die younger do so not because they are fatter but because they have a more severe form of diabetes.  So the conclusion that people should eat less to extend life remains essentially "not proven".

Body-Mass Index and Mortality among Adults with Incident Type 2 Diabetes

By Deirdre K. Tobias et al.


The relation between body weight and mortality among persons with type 2 diabetes remains unresolved, with some studies suggesting decreased mortality among overweight or obese persons as compared with normal-weight persons (an “obesity paradox”).

We studied participants with incident diabetes from the Nurses' Health Study (8970 participants) and Health Professionals Follow-up Study (2457 participants) who were free of cardiovascular disease and cancer at the time of a diagnosis of diabetes. Body weight shortly before diagnosis and height were used to calculate the body-mass index (BMI, the weight in kilograms divided by the square of the height in meters). Multivariable Cox models were used to estimate the hazard ratios and 95% confidence intervals for mortality across BMI categories.

There were 3083 deaths during a mean period of 15.8 years of follow-up. A J-shaped association was observed across BMI categories (18.5 to 22.4, 22.5 to 24.9 [reference], 25.0 to 27.4, 27.5 to 29.9, 30.0 to 34.9, and ≥35.0) for all-cause mortality (hazard ratio, 1.29 [95% confidence interval {CI}, 1.05 to 1.59]; 1.00; 1.12 [95% CI, 0.98 to 1.29]; 1.09 [95% CI, 0.94 to 1.26]; 1.24 [95% CI, 1.08 to 1.42]; and 1.33 [95% CI, 1.14 to 1.55], respectively). This relationship was linear among participants who had never smoked (hazard ratios across BMI categories: 1.12, 1.00, 1.16, 1.21, 1.36, and 1.56, respectively) but was nonlinear among participants who had ever smoked (hazard ratios across BMI categories: 1.32, 1.00, 1.09, 1.04, 1.14, and 1.21) (P=0.04 for interaction). A direct linear trend was observed among participants younger than 65 years of age at the time of a diabetes diagnosis but not among those 65 years of age or older at the time of diagnosis (P<0.001 for interaction).

We observed a J-shaped association between BMI and mortality among all participants and among those who had ever smoked and a direct linear relationship among those who had never smoked. We found no evidence of lower mortality among patients with diabetes who were overweight or obese at diagnosis, as compared with their normal-weight counterparts, or of an obesity paradox.

N Engl J Med 2014; 370:233-244

A fat old age?

If you are a mouse

CARBS have come in from the cold, with a new study showing that a high-carbohydrate, low-protein diet can help you live longer.

The downside is it will also make you fat.

Sydney University research to be released today found that mice fed a high-carbohydrate, low-protein diet had a longer lifespan and better cardiometabolic health - despite being overweight.

While the study found that a high-protein, low-carbohydrate diet resulted in reduced body fat and food intake, it also led to a shorter lifespan and poor cardiometabolic health.

Darwin health and safety worker Maurice Moore, 58, eats half a loaf of bread every day. "I don't eat it all in the one sitting; I usually have a banana wrapped in bread, asparagus wrapped in bread and peanut butter and strawberry jam on bread," he said.

"I just did a medical for work and scored 96/100, all I needed to pass was 44/100." Mr Moore said he has "never taken a (sick) day off work in (his) life".  "I had a cold in 2011 but that was it," he said.

The study, which could lead to new drugs to control appetite and increase lifespan, compared the effects of 25 different diets in mice.  And it confirmed the fat-reducing effects of low-protein diets.

"The reason most diets fail is because the body's protein target is so potent," co-author Professor David Le Couteur said.

Once the mice in the study satisfied their need for protein, they started to reduce their food intake.

The authors suggest that a diet that consists of 15-20 per cent high-quality protein, low in fat and high in good-quality carbohydrate will deliver the best metabolic health and longest life.

The research, published in the journal Cell Metabolism, also suggests that lifespan could be extended by manipulating the ratio of macronutrients in the diet.

"This research has enormous implications for how much food we eat, our body fat, our heart and metabolic health, and ultimately the duration of our lives," said Professor Steve Simpson. "We have shown calories aren't all the same. We need to look at where they come from and how they interact."


No comments: