The Impact of Nutrition on Physical and Mental Health

Last week, on April 3rd, 2019, an international consortium of researchers, the „Global Burden of Disease 2017 Diet Collaborators“, published an important metaanalysis entitled „Health effects of dietary risks in 195 countries, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017“ in the Lancet.

The authors systematically estimated the disease-specific burden of 15 different dietary risk factors among adults aged 25 years or older, and expressed them as their effects on mortality and „disability-adjusted life years“ (DALYs, a measure of impairment of health by a disease). They calculated those numbers for each of 195 countries.

For their calculation the authors used the intake of each dietary factor (e.g., fruit consumption), the effect size of the dietary factor on disease endpoint, and the level of intake associated with the lowest risk of mortality, based on the available scientific evidence. A huge amount of data had to be taken together.

The impact of the following 15 dietary risk factors for non-communicable diseases were estimated (with optimal levels, ranges of intake in brackets):

Diet low in fruits: 250 g (200 – 300 g) per day

Diet low in vegetables: 360 g (290 – 430 g) per day

Diet low in legumes: 60 g (50 – 70 g) per day

Diet low in whole grains: 125 g (100 – 150 g) per day

Diet low in nuts and seeds: 21 g (16 – 25 g) per day

Diet low in milk: 435 g (350 – 520 g) per day

Diet high in red meat: 23 g (18 – 27 g) per day

Diet high in processed meat: 2 g (0 – 4 g) per day

Diet high in sugar-sweetened beverages: 3 g (0 – 5 g) per day

Diet low in fibre: 24 g (19 – 28 g) per day

Diet low in calcium: 1.25 g (1.00 – 1.50 g) per day

Diet low in seafood omega-3 fatty acids: 250 mg (200 – 300 mg) per day

Diet low in polyunsaturated fatty acids: 11% (9 – 13%) of total daily energy

Diet high in trans fatty acids: 0.5% (0.0 – 1.0%) of total daily energy

Diet high in sodium: 3 g (1 – 5 g) per day

On a global level – but with large regional differences – dietary risk factors were responsible for 11 million deaths and 255 million DALYs. 11 million deaths per year represent 22% of all deaths, which means that one fifth of all deaths have to be ascribed to poor nutrition! Cardiovascular disease was by far the leading cause of diet-related deaths (10 million), followed by cancer (900,000) and type 2 diabetes (350,000).

The authors state that “globally, consumption of nearly all healthy foods and nutrients was suboptimal in 2017”. The largest discrepancies between current and optimal levels of intake were documented for nuts and seeds, milk, and whole grains. The consumption of nuts was just 12% of the optimal level, that of milk 16% and of whole grains 23%. On the other hand, intake of unhealthy foods was much higher than recommended. The consumption of sugar-sweetened beverages was 49 g per day (instead of the recommended 3 g, see above), that of processed meat was 4 g per day, sodium intake was 6 g per day.

The study presents a lot of very interesting numbers and illustrations. For example, Germany (and the USA) belongs to the ten countries in which low intake of whole grains is the leading dietary risk factor for deaths and DALYs.

The paper is published with open access, it can be found here. There is also a lot of supplementary material available here. It is probably the most important paper yet that documents the importance of diet for physical health. Unfortunately, mental health is not addressed in the present paper. I have emphasized the relevance of nutrition for mental health in my blog post of August 1st, 2017, which was entitled “Nutrition: a mega theme for psychiatry of the future“. The New York Times also highlighted this topic a few days ago (March 28, 2019) in an article “Can what we eat affect how we feel?”. Certainly! There is no doubt about it. In that article, which can be found here, the Columbia University psychiatrist Dr. Drew Ramsey is cited. “Dr. Ramsey argues that a poor diet is a major factor contributing to the epidemic of depression, which is the top driver of disability for Americans aged 15 to 44, according to a report by the World Health Organization.” And further: “A survey published in 2017 by the Centers for Disease Control and Prevention  reported that only one in 10 adults meets the minimal daily federal recommendations for fruit and vegetables — at least one-and-a-half to two cups per day of fruit and two to three cups per day of vegetables.“

In the New York Times article a number of studies is referenced that support the notion that nutrition is as important for mental as it is for physical health. For example, a study that was published in 2016 in the American Journal of Public Health showed that you don’t have to wait for years or even decades to demonstrate the health benefits of food (Mujcic and Oswald, Am J Public Health. 2016;106:1504–1510). The study in 12,000 Australians showed that happiness, life satisfaction, and well-being are a function of fruit and vegetable consumption, and that changes can be shown within two years.

The authors of the Lancet paper conclude their analysis as follows: “In summary, we found that poor dietary habits are associated with a range of chronic diseases and can potentially be a major contributor to NCD [non-communicable diseases] mortality in all countries worldwide. This finding highlights the urgent need for coordinated global efforts to improve the quality of human diet. Given the complexity of dietary behaviours and the wide range of influences on diet, improving diet requires active collaboration of a variety of actors throughout the food system, along with policies targeting multiple sectors of the food system.”