Evidence supports the incorporation of nuts in the diet

I spent last week in Portugal, and while I was there my girlfriend and I had a lot of food given to us by local farmers. We were lucky enough to be given quite a stash of fresh produce including citrus fruit, onions, broad beans, fresh peas, lettuce and cabbages. We were also given a carrier bag full of walnuts in their shells. The shelling kept us busy, but the end result was worth it: for a few days we had fresh, tasty walnuts that we used as a snack food and pre-dinner nibble for family and friends.

I like to eat nuts, not just because I like their taste and texture, but also because for me (like for a lot of people) they do a decent job of quelling my appetite. That’s a useful property to have in a snack or pre-meal nibble, if part of the reason for you eating it is to stop your appetite running out of control at mealtime. The sating effect of nuts is at least in part related to their relatively high-protein nature.

However, nuts have other things going for them in that they have relatively low glycaemic index, and therefore tend not to stimulate much in the way of secretion of insulin (the chief fat storage hormone), and help to stimulate the metabolism. These and other factors may help to explain why studies have found that, generally speaking, nuts are not a fattening food despite being intensely calorific.

Further support for this notion came from a meta-analysis (analysis of several similar studies) on the effect of walnut eating on measures of health [1]. 13 studies where included in the review, and each study involved individuals consuming 10-24 per cent of their calories in the form of walnuts over 4-24 weeks. Taking the evidence of all studies together, there was not evidence that walnut eating led to a significant change in weight.

This study also looked at the effect of walnut eating on specific blood fat levels including supposedly unhealthy low density lipoprotein (LDL) cholesterol. Walnut eating led to a reduction in the levels of this fat. It did not, however, lead to significant changes in the levels of supposedly healthy high density lipoprotein (HDL) cholesterol or triglyceride levels.

If we were to interpret these results from a traditional perspective, we would say that overall, the evidence suggests that walnut eating leads to an improvement in cardiovascular risk factors. As the authors point out, longer-term studies would be useful for helping to verify this finding.

However, I think it is worth bearing in mind that nuts are generally rich in a range of nutrients that might have benefits for cardiovascular health, including monounsaturated fat, magnesium, potassium, copper and vitamin E. Walnuts are also quite rich in a form of omega-3 fat known as alpha linolenic acid which might also have benefits for cardiovascular health. There is indeed some evidence which links nut eating with benefits in this respect: One study found that women consuming at least five ounces (about 125 g) of nuts each week had one-third fewer heart attacks compared to women who rarely or never ate nuts [2]. In another study, men eating nuts twice a week, compared to those who rarely or never ate nuts, were found to be at about half the risk of ‘sudden cardiac death’ [3].

References:

1. Banel DK, et al. Effects of walnut consumption on blood lipids and other cardiovascular risk factors: a meta-analysis and systematic review. Am J Clin Nutr (May 20, 2009). doi:10.3945/ajcn.2009.27457

2. Hu FB, et al. Frequent nut consumption and risk of coronary heart disease in women: prospective cohort study. BMJ 1998;317(7169):1341-5

3. Albert CM, et al. Nut consumption and decreased risk of sudden cardiac death in the Physicians’ Health Study. Archives of Internal Medicine 2002;162(12):1382-7

11 Responses to Evidence supports the incorporation of nuts in the diet

  1. Adam Steer - Better's Better blog 21 May 2009 at 11:35 pm #

    Hey Doc,

    I certainly agree that a calorie is not a calorie and that nuts can be an excellent addition to the diet. But a lot of people tend to take that as a license to eat them without limit. And in the end, calories do count in the big picture. So I think you have to add a caveat when telling someone – especially someone looking to control or lose fat – that nuts should be eaten in moderation. Of course, if bodyfat isn’t an issue, this point becomes moot.

    Cheers,
    Adam

  2. Anna Salvesen 22 May 2009 at 7:51 pm #

    Having to shell the nuts first is a great way to limit consumption. Fresher, too.

  3. simona 23 May 2009 at 1:49 am #

    You were lucky to get the real thing and possibly from last year’s crop. Over here (Ireland) it’s hard to find walnuts that are fresh; because of the PUFA content and maybe because of handling and storage they go rancid very quickly.

  4. Bill Cockerill 23 May 2009 at 12:27 pm #

    Adam,

    I would challenge your advice that you should eat nuts in moderation. It’s worth trying to binge on nuts – eat as many as you can. Try this with meat or cheese too and you won’t get very far and soon get very full. By contrast gorging on carbs is easy (and a pleasure!) and with the spike in insulin you’ll soon be ready for more when it crashes back down. Gary Taubes covers this myth and many others in his excellent book The Diet Delusion that is about the science behind diet and obesity.
    http://en.wikipedia.org/wiki/Gary_Taubes

    Bill

  5. Wendy 24 May 2009 at 8:31 pm #

    I am seeing so much about including nuts in your diet, however, I have to ask the question – what should people with a nut allergy do ? Do we have to go without these health benefits or is there an alternative for us ?

  6. Dr John Briffa 25 May 2009 at 5:25 am #

    Wendy

    I think seeds (e.g. pumpkin, sesame, sunflower) are a reasonable swap for nuts (assuming no allergy to these, either).

  7. Chris 31 May 2009 at 11:42 am #

    Hey Adam,
    point taken, it is possible to overindulge in nuts just as it it possible to overindulge in fats, oils, sugar, or energy dense carbohydrate staples such as bread, pasta, rice or potatoes.
    However, the point being made about the inclusion of nuts in a suitably varied diet is the possibility that nuts may assist the metabolic function of the body to self-regulate appetite. Walk down any high street and observe that many people appear to have lost the ability to self regulate their appetite. So the question is why, exactly. Nuts have been a potential and probable food source for humans and our progenitors for millions of years, they contain carbohydrate and protein in a balance along with generous amounts of fibre, plus the minerals and nutrients described. For a forager, they rank as quite energy dense and satiating compared to the available alternatives.
    Nuts however, are not so energy dense as the simple and refined carbohydrates that proliferate in a typical modern western diet and do not therefore contribute so significantly to hyperinsullinemia.
    Perhaps before too long we will get the study(ies) the developed world needs to support the common sense (but seemingly not fully verified) notion that hyperinsullinemia arising from a diet of unnaturally high GL is a factor contributing to the loss of self-regulation of appetite. S Boyd Eaton presents a good argument in this paper;
    http://www.cast.uark.edu/local/icaes/conferences/wburg/posters/sboydeaton/eaton.htm
    and the book ‘The 7-day Zone Diet, auth. Barry Sears gives a comprehensible argument, with explanation of the process, for the balanced consumption of protein and carbohydrate to the end of better regulation of insulin. At 30kg overweight I belong to the target audience. I can testify that once the issue of hyperinsullinemia is addressed then appetite and portion control are more easily managed. Accordingly, I am now just 23kg overweight without counting calories and without adherence to ‘low-fat’ noble myth.
    Modern civilisation is founded upon the ability of humans to get energy from food quickly so that our time is free for other pastimes and occupations – we even use the term ‘fast-food’. Given rising rates of obesity and diabetes is it time to question have we crossed a line in the sand and where in the sand does the line lie?

  8. Trinkwasser 7 June 2009 at 9:46 pm #

    Eat too many carbs, spike your insulin, and as it drops a few hours later you are driven to eat more carbs all over again.

    Quite apart from the satiety factor I find nuts to have a built in control factor: eat too many (and pseudonuts like peanuts and cashews are even worse) and I will blow off like a carthorse . . .

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