The passage from diet to disease

The passage from diet to disease

Humans have challenged the permanency of disease with advanced research techniques and sophisticated medical technology. However, there is still a long list of conditions that remain chronic. While we can say that genetic diseases are ‘fated’ and infectious diseases are ‘afflicted’, the way we eat and live our lives plays a significant role in the occurrence of non-communicable diseases.

What are the non-communicable diseases?

Non-communicable diseases (NCDs) are lifestyle diseases. Bad life choices such as smoking cigarettes, drinking like a sailor, and a see-food-and-eat-it diet, could trigger a chronic illness such as cancer, liver disease, or type 2 diabetes. According to the World Health Organization, NCDs are the No. 1 killer in society. While significant, bad-life choices are just one catalyst for NCDs, environmental factors, socioeconomic status, and genetic predisposition all interplay and put some people in a higher danger zone than others.

Non-Communicable diseases and dietary factors

For adults, a big part of lifestyle they are in control of is nutritional choices. Dietary choices matter when it comes to the prevention of NCDs.

Science has repeatedly found that a diet too heavy or light in dietary factors – e.g. high in sugar or high trans-fats, low in vegetables or fruits – can be linked with non-communicable diseases, e.g. type 2 diabetes and heart disease. Findings from these studies have shaped national and international nutritional daily recommended intakes of dietary factors.

The knowledge gaps

What we know about the link between dietary and NCDs comes from long-term prospective observational studies (because hindsight is a beautiful thing). Short-term trials with intermediate outcomes, e.g. affect of sub-optimal intake of major food groups or nutrients on blood pressure, body weight, represents the second information source.

Diet-disease studies have generally focused on a small pocket of society, and this has left health professionals wondering whether the diet-effect translates to the general population.

The big-picture GBD study 2017

Global Burden of Diseases, Injuries, and Risk Factors Study (GBD, published in 2019) collaborators have filled in the diet-disease knowledge gaps.

Researchers gathered information on people’s dietary habits of 15 major food groups and nutrients over 16 years from across 195 countries.

What did people’s dietary habits look like in 2017?

Not good. Globally, people were not eating enough food from the healthy food groups. The intake of nuts and seeds, milk, and whole grains were all sub-optimal, at only 12%, 16%, and 23% of the optimal intake, respectively. In contrast, people were over-indulging in ‘bad’ foods, specifically in sugary beverages, processed meats, salt, and red meat. Males ate more than females overall of both the good and bad foods, as did middle-aged people (50-69 years) compared to young adults (25-49 years).

Diets were sub-optimal in 21 out of the 22 regions included in the study. However, people in central Asia were eating their veggies; the wealthy folk in high-income Asia-Pacific included enough omega-3s fatty acid seafood; and those in the Caribbean, tropical Latin America, and eastern sub-Saharan Africa hit their recommended intake of legumes.

On the flip side, nearly every region had a diet too high in salt and sugary beverages. Those in New Zealand and Australia, southern Latin-America, and tropical Latin-America over-ate red meat.

Processed meats were popular among the rich in North America and the Asia Pacific, as well as in Western Europe. The intake of trans fats was highest in high-income North America, central Latin America, and Andean Latin America.

What were the trends in diet, disease, morbidity, mortality?

GBD scientists estimated that in 2017 dietary risks were responsible for 10-12 million deaths (22% of all deaths among adults) and 234-274 million DALYs (15% of all Disability Adjusted Life Years – DALYs) – see graphic.

(DALYs – Disability Adjusted Life Years – is a standardised measurement of the burden of disease. The top figure shows when an individual was born. The first gold strike in the life timeline represents the time at which the individual developed a disease. The individual lived with the disease until the silver strike, when he died, well before the expected age of death. In simple terms, DALYs quantify the number of years lived with a disease and the number of years lost due to death. The worst disease-offenders were cardiovascular disease, cancer, and type 2 diabetes. Diet-related mortality and morbidity mostly affected people aged between 25-70 yrs.)

What diet-related deficiencies contributed to the burden of disease?

A small group of dietary risks were behind most of the diet-related health effects. In 2017, a high-salt diet attributed to more than half of the diet-related deaths (1-5 million), and two-thirds of the diet-related DALYs, 34-118 million DALYS. A low intake of whole grains and fruits was attributable to 2-4 million deaths and 59-109 DALYs, and 1-4 million deaths and 41-92 DALYs, respectively. A suboptimal intake of whole grains explained the most deaths among women and those aged between 25-50, and high-salt intake was to blame for the deaths amongst males and people aged 70 years and above.

Socio-demographic factors?

Choice and education are both luxuries. Global Burden of Diseases, Injuries, and Risk Factors Study researchers found a link between diet-related mortality and morbidity and socio-demographic index. (SDI is a measure of a country’s development progress. Income per capita, mean educational attainment of people aged 15 and over, and total fertility rate among women younger than 25 are factors used to calculate it.) Low SDI regions had the highest burden of exposure to dietary risks.

The GBD collaborators’ conclusions

1. A poor diet is associated with several chronic illnesses.

2. A shift to a well-balanced, healthy diet could prevent one in five deaths globally.

3. The effects of diet on disease do not discriminate – a sub-optimal diet caused health effects for people of all ages, sexes, and socio-demographic groups.

4. NCDs were primarily associated with high salt, or low in whole grains, nuts and seeds, fruit, vegetables, and omega-3 fatty acids.

5. A diet high in sodium, low in whole grains, or low in fruits are most strongly associated with global deaths and DALYs from cardiovascular diseases, type 2 diabetes, and cancers.

6. A poor diet is more deadly than any other disease risk factor, including smoking tobacco.

7. A shift from a predominately animal-based diet to a plant-based diet is not only better for you but also better for the environment.

8. Disease-prevention campaigns are effective at educating people about the diet risks associated with NCDs, e.g. sugar and type 2 diabetes. However, there is a need to inform people of the health impacts of other dietary risks, such as a diet low in whole grains and fruits.

9. While this study helped to reveal the diet-disease big picture, we will require further research to understand the diet-disease relationships due to the complexity of the interactions at a population-level.

Take-home message

Remember, you are the captain of your ship. Eat well for a better shot at a long, healthy, and happy life!

Access the full article at: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)30041-8/fulltext

Literature cited

1. World Health Organization, 2019. Non-communicable diseases. Retrieved from https://www.who.int/gho/ncd/en/.

2. U.S. National Library of Medicine, 2019. What does it mean to have a genetic disposition? Retrieved from https://ghr.nlm.nih.gov/primer/mutationsanddisorders/predisposition.

3. GBD 2017 Diet Collaborators, 2019. Health effects of dietary risks in 195 countries, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017. The Lancet, 393(10184), 1958-1972. DOI: https://doi.org/10.1016/S0140-6736(19)30041-8.

4. Forouzanfar, M. H. and Alexander, L. et al., 2013. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks in 188 countries, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2015; 386: 2287-2323.

5. GBD 2015 Risk Factors Collaborators. 2016. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015. Lancet. 2016; 388: 1659-1724

6. Tilman, D., and Clark, M., 2014. 2014. Global diets link environmental sustainability and human health. Nature, 515:518-522