Fried and grilled meat may raise risk of diabetes and dementia

Why is ageing research so important?

As a nation we are ageing rapidly and according to the World Health Organisation the proportion of people aged 60 years and over is growing faster than any other age group in almost every country. One clinical implication of growing older is the risk of experiencing age-related diseases including neurological disorders, dementia and Alzheimer’s disease, type 2 diabetes, various cancers, osteoporosis and other serious conditions. Considerable research has therefore focused on understanding the underlying mechanisms involved in ageing with the aim of leading longer but also healthier lives.

Effects of calorie restriction on ageing

It has been known for a long time now that calorie restriction (decrease in caloric intake over time) increases both longevity (longer life) and improves health in rodents, monkeys and humans. Whilst it is still not completely clear how this happens, it is also known that many people are unlikely to want to or be able to cut down on their caloric intake over the lifetime. Furthermore, a recent report from the long-term follow-up of calorically restricted monkeys suggests that perhaps genetics and other factors such as constituents of the diet may be more important than simply cutting down on calories.

What are the effects of other diets on ageing and dementia?

A recent article published in the Guardian (25th Feb 2014) reports on a new study entitled “Fried and grilled meat may raise risk of diabetes and dementia”, which investigates how certain diets or constituents of the food may have an adverse effect on ageing and health. This study examined the effects of methyl-glyoxal derivatives (MG) present in the diet and how this impacts on development of Alzheimer’s disease (AD) and diabetes. These glycotoxins or advanced glycation end products (AGEs) are a class of agents implicated in diabetes, ageing and AD. The authors of this study designed their experiments so that they changed the amount of these MGs in the rodent diet. They used aged rodents (18 months old or 24-26 months old), thus mimicking what may be happening during middle- or old-age in humans. They then fed the 18 month old mice diet which had MG present in it (MG+) versus diet which had MG taken away from it (MG-). They compared these mice in regards to their diabetic status and cognitive function to old-age mice (24-26 months). The first interesting thing that is transparent from this work is that even though these mice were “pair-fed”, which means that they were given exactly the same amount of food to eat to ensure that neither is calorically restricted or overfed, the MG+ mice weighed significantly more than the MG- mice. Serum insulin levels were also two times higher in MG+ mice, thus suggesting that they started developing signs of type 2 diabetes. At the same time, these mice also showed poor performance in their cognitive tests and motor activity and were more similar to old-age (24-26 month) animals.

To translate their findings into the context of what may be happening in humans, they had assessed 93 human volunteers from New York for their serum MG levels, cognitive function and diabetic status and examined these again 9 months later. Interestingly, they found that increased serum MG levels in the human volunteers were associated with a decrease in their cognitive function over time. They also found that these were closely associated with the development of insulin resistance, an indicator of development of type 2 diabetes, at the same time. They therefore suggested that decreasing the amount of these MGs in the diet may have an important public policy and health potential.

What did the media say about this?

The Guardian article correctly reports the findings from the current study but also points out that the lead author states that “the question that needs to be answered is whether cutting down on glycotoxins can prevent or reverse dementia”. They also point out that these glycotoxins (in other words MGs) are widespread in animal products, including meat and dairy produce that we consume every day and need for normal function, and that levels increase when food is fried, grilled, pasteurised or smoked. However, the headline statement that the “Fried and grilled meat may raise risk of diabetes and dementia” is not really something new or novel; we all know that eating fried or grilled food also has an increased risk of fats in diet in the case of fried food and that grilling/barbequing food increases carcinogenic substances in the food. One thing that could be explored further is the balance of eating healthy foods versus normal portion size. We still don’t know how high or low our intake of MGs has to be to see these reported negative effects or indeed if we can reverse these bad effects of MGs in our diet by switching to MG-low foods. It is also quite unclear if MG-low foods have any negative effects on health long-term as these are all relatively short studies. The article is very correct to point out that for the scientific community, the exciting part of the study is that it provides a suggested mechanism how AD and diabetes may be linked and it is down to the scientists to tease these out and test further.

Cai W, Uribarri J, Zhu L, Chen X, Swamy S, Zhao Z, Grosjean F, Simonaro C, Kuchel GA, Schnaider-Beeri M, Woodward M, Striker GE, Vlassara H. (2014). Oral glycotoxins are a modifiable cause of dementia and the metabolic syndrome in mice and humans.. Proc Natl Acad Sci U S A. doi: 10.1073/pnas.1316013111.