What is it about nuts that may help those with metabolic syndrome?

Metabolic syndrome is a term used to describe a constellation of supposed risk factors for disease including excess weight around the midriff (abdominal obesity), raised blood pressure, raised levels of blood fats known as triglycerides and raised blood sugar. The condition is associated with an enhanced risk of cardiovascular disease (heart disease and stroke) as well as type 2 diabetes. Another common feature of metabolic syndrome is raised levels of insulin. This is not surprising when one considers that insulin can drive abdominal obesity, raised blood pressure and triglyceride manufacture in the liver. High levels of insulin can also lead to ‘insulin resistance’ (a state where the body becomes somewhat ‘numb’ to the effects of insulin), which can then lead to raised blood sugar levels.

Because insulin looks like a key factor in metabolic syndrome, it makes sense to take a nutritional approach to this condition that helps temper insulin levels in the body. What this means in practice is a diet low in carbohydrate sources that tend to be disruptive for blood sugar and therefore insulin. Foods that are generally worth eliminating/limiting in the body include those sweetened with refined sugar as well as most forms of bread, potatoes, rice, pasta and breakfast cereals. The rationale for this approach and the evidence for it was recently explored in a review published in the Scandinavian Cardiovascular Journal [1].

The reason that this is important is because many individuals with metabolic syndrome either take it upon themselves or are advised to cut back on fat in their diet. The problem is that this almost inevitably leads to increased carbohydrate consumption. Perhaps not surprisingly, in practice this approach tends not to work so well. In fact, in my experience is that it quite frequently compounds the issue.

This week saw the publication of a study that assessed the effects of three diets on individuals with metabolic syndrome. One of these diets was a low-fat diet, the other two diets were based on the Mediterranean diet. In one group the Mediterranean diet was supplemented with olive oil (1 litre a week). The Mediterranean diet-eating group were instructed to eat 30 g of mixed nuts each day. The study lasted for a year.

At the end of the year, the researchers discovered that 2 per cent of individuals eating the low-fat diet had reversed their metabolic syndrome to the extent that they no long appeared to have metabolic syndrome. However, those eating the Mediterranean-based diets fared significantly better: rates of metabolic syndrome fell by about 7 and 14 per cent in the olive oil and nut supplemented groups respectively. Compared to eating the low fat diet, eating the Mediterranean diet plus buts enhanced the chances of reversal of metabolic syndrome by 70 per cent, and this was statistically significant. In short, in this trial of treatments for metabolic syndrome, the Mediterranean diet plus nuts was the winner, and the low-fat diet the loser.

One advantage of a Mediterranean diet compared to a standard low-fat one is that because there is not explicit restriction of fat, blood sugar disruptive carbohydrates can be somewhat de-emphasised in the diet. This is clearly a boon for individuals with metabolic syndrome. But what’s the deal with nuts? Why should nuts be seemingly so beneficial for individuals with metabolic syndrome? Well, for a start nuts are generally very undisruptive regarding blood sugar levels. But them again, so is olive oil, and the diet enriched with this did not perform as well as the one enriched with nuts.

Looking more deeply into nuts we know that they are rich in certain nutrients that olive oil may not offer. For me, the stand-out nutrient that is likely to have relevance to those suffering from metabolic syndrome is magnesium. This nutrient plays a part in blood sugar balance and insulin function in the body. There are also several studies now that link higher intakes of magnesium with lower risk of metabolic syndrome [3-5]. And even some evidence which has found magnesium supplementation helps blood sugar control and the effectiveness of insulin in type 2 diabetics (which can be preceded by metabolic syndrome) [6]. That amounts, in my mind, to a fair amount of evidence that suggests that a key nutrient through which nuts exert their beneficial effects in metabolic syndrome is magnesium.

References:

1. Feinman RD, et al. Carbohydrate restriction as the default treatment for type 2 diabetes and metabolic syndrome. Scand Cardiovasc J. 2008;42(4):256-63.

2. Salas-Salvadó J, et al. Effect of a Mediterranean Diet Supplemented With Nuts on Metabolic Syndrome Status: One-Year Results of the PREDIMED Randomized Trial. Arch Intern Med. 2008;168(22):2449-2458.

3. McKeown NM, et al. Dietary magnesium intake is related to metabolic syndrome in older Americans.Eur J Nutr. 2008;47(4):210-6.

4. Song Y, et al. Magnesium intake, C-reactive protein, and the prevalence of metabolic syndrome in middle-aged and older U.S. women. Diabetes Care. 2005;28(6):1438-44.

5. He K, et al. Magnesium intake and incidence of metabolic syndrome among young adults.
Circulation. 2006;113(13):1675-82.
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6. Rodríguez-Morán M, et al. Oral Magnesium Supplementation Improves Insulin Sensitivity and Metabolic Control in Type 2 Diabetic Subjects: A randomized double-blind controlled trial. Diabetes Care2003;26:1147-1152.