Richard Smith: We don’t know what to eat
28 Oct, 09 | by julietwalker
WHO is currently setting priorities for research in chronic or non-communicable disease, and generally the first research question is “Will what has worked in rich countries work in low and middle income countries?” We know, for example, what to do to reduce deaths from heart disease and how to reduce tobacco consumption. But interestingly when it comes to nutrition we don’t know what to recommend. The advice for rich countries may be wholly inappropriate for poor countries.Let’s start with fat. WHO recommends that fat should not be more than 15-30% of dietary energy and saturated fat 10%. These recommendations were made years ago, when fat accounted for well over 30% of the diet in rich countries. Those who made the recommendations knew well that lower fat consumption meant lower rates of heart disease right down to countries like India, where fat was well under 10%. Indeed, you need a certain level of fat consumption for smoking and hypertension to have their damaging effects—they needed fats to create the atheromatous plaques. Similarly intakes of saturated fat under 5% are good for health.
The 30% figure for total fat and 10% for saturated fat were pragmatic, much better than fat consumption in most rich countries but achievable. The lower figure for total fat was equally pragmatic: at that time many countries had a figure for total fat close to that and very little heart disease. Unfortunately these figures have become fixed in the heads of policy makers with them thinking that 30% fat and 10% saturated fat are targets and that there is no need to worry until they are reached. In fact low and middle income countries should probably aim for 15% total fat and 5% saturated fat, although we don’t know for sure.
Then there is the problem of sugar. WHO recommends that added sugar shouldn’t be more than 10% of dietary energy, but sugar and fat probably interact in ways that we don’t fully understand. Thus countries in the Caribbean that where sugar intakes are over 20% have obesity rates far higher than would be expected from their total fat intake. Probably what matters is the “energy density” of foods: fat and sugar both contribute to energy density as does refining foods. We don’t know what levels of energy density to recommend for poorer countries, but the level of sugar intake should probably be 5% of dietary energy not 10%.
Another complication is that many people in the poor world may be “supersensitive” to the effects of fat and sugar. We know that South Asians have much higher rates of diabetes and obesity than Europeans for the same intake of fat. It’s probably true for Mexicans and perhaps other populations as well. This may well be the result of the Barker hypothesis that those whose mothers were malnourished when pregnant are much more likely to develop diabetes, hypertension, and cardiovascular disease. The brutal reality is that until recently some 40-60% of people in the developing world were malnourished, and the very high rates of diabetes in China might be the result of extensive famine in China decades ago. Probably recommendations on fat, sugar, and salt intake should be more stringent in low and middle income countries.
There are many other unresolved issues in nutritional advice, and the subject is complicated further by usually very poor data on what people actually eat in low and middle income countries.
So the research issues around nutritional advice in low and middle income countries are much more complicated than simply finding ways to implement what we already know: there’s a great deal that is hugely important that we don’t know.
WHO can definitely do with some rethinking of their recommendations. Just a couple of thoughts on your post Richard:
You wrote:
“Thus countries in the Caribbean that where sugar intakes are over 20% have obesity rates far higher than would be expected from their total fat intake”.
That’s because it’s sugar (carbohydrates) that makes people fat - it isn’t fat that makes people fat.
And you wrote:
“We know that South Asians have much higher rates of diabetes and obesity than Europeans for the same intake of fat.”
That’s because diabetes is nothing to do with fat and everything to do with carbohydrates.
Anne
October 30th, 2009 at 4:30 pm
Richard
There’s one very easy part to improving nutrition, and that is salt reduction. Almost everyone in the developed and developing world alike eats several times more salt than they need with enormously adverse consequences for chronic disease. While we argue about the other components we could get on with salt reduction which promises to be highly cost-effective. With very large net health gains almost irrespective of the level of income of the setting in which it is applied.
Cheers
Bruce
Bruce Neal
November 2nd, 2009 at 10:55 am
I posted this blog on a listserve we have for around 200 researchers into chronic disease in low and middle income countries, many of whom are nutritionists. A spirited debate followed on whether we knew what to advise on nutrition in low and middle income countries or whether we needed much more research.
This very useful contribution came from Walter Willett, a famous professor of nutrition at Harvard. He gave me permission to post an edited version.
“The WHO adviser has a huge blind spot for the adverse effects of large amounts of refined carbohydrate that have become the major source of calories for most of the world’s population, even rural areas of poor countries. This is the consequence of persistence in focusing on total fat as a major cause of obesity and a primary objective of dietary advice. This has been refuted by many lines of scientific evidence that are reviewed comprehensively in the recent FAO review of dietary fats, which concludes that the type of fat has major implications for health, but that low total fat intake should not be a dietary goal.
Unfortunately, the adviser has caused serious damage in developed countries by promoting low fat, high carbohydrate diets and seems intent of doing this to developing countries as well. He also strongly promotes “energy density” as a primary target, but the reality it that this has not been supported by long term studies: indeed, it has been refuted by the Women’s Healthy Eating and Living (WHEL) study.
Most would agree that many foods, such as highly processed
fast foods that have high energy density are not healthy, but there are also many very healthy foods such as nuts, seeds and whole grain breads that are high in energy density and these have not been associated with weight gain. This is potentially a dangerous path to promote because the food industry knows very well how to reduce the energy density of foods high in sugar and refined starches just by adding water, and they can readily market these as healthy choices just as they did with low fat products based on these same ingredients.
The initial question “What is a healthy diet?” is extremely important because we often use “eat a healthy diet” as a throw-away piece of advice. While there are many details to resolve (and I agree that the role of dairy products is an important one) we do have a huge amount of data to support the basic elements of a healthy global diet that would apply to almost every population worldwide:
Carbohydrates should be primarily from whole grains—Intake of sugar should be low, and sugary beverages should be avoided—Fats should be primarily from non hydrogenated vegetable oils—Intake of red meat should be at most occasional and protein should be mainly from legumes and nuts, with modest amounts of poultry, fish, and eggs and (optionally) dairy products. —At least 2-3 servings of vegetables daily, with more being desirable—Sodium intake should be reduced slowly to less than 2500 mg/d.
I suspect that very few nutritionists would disagree with these elements, and there is really no need to get into arguments about the exact percentages of total fat or carbohydrate (and there are really no data to support a specific percentage). This diet (which is consistent with what I eat) can be produced sustainably in almost every part of the world including the poorest villages in Africa and can be prepared with an enormous range of flavors and cuisines.
Again, we do have work to do in refining some details, but that should not distract us from moving toward what we know is a healthy direction. This seems simple, but the distance between this healthy global diet and what populations almost everywhere are actually consuming is huge and not getting smaller.”
Richard Smith
November 16th, 2009 at 1:26 pm