Gene-Editing Bananas

Bananas are a staple food in many low- and middle-income countries; however, many have a virus within – the Banana Streak Virus (BSV). This virus is integrated inside the DNA of the banana’s genome and becomes active when the banana plant is stressed by heat or drought, which can result in the destruction of the entire plantation. It can also be triggered through propagation methods, meaning BSV is a major constraint in banana breeding programmes. Researchers from the International of Tropical Agriculture in Kenya recently used CRISPR gene editing to inactive the virus, resulting in 75% of edited bananas remaining asymptomatic when placed in stressful conditions (compared to non-edited controls).[1] It is hoped that not only we can use these edited plants to breed virus-free plants for farmers, but we can also utilise the technique to safeguard the future of the Cavendish variant of bananas. Cavendish bananas account for the vast majority of bananas in international trade, but they are threatened by Tropical Race 4 a fungal disease. As the Cavendish is sterile, it is not possible to breed resistant varieties, so CRISPR editing offers an opportunity to introduce resistance.

— Peter Chilton, Research Fellow

Reference:

1. Tripathi JN, Ntui VO, Ron M, et al. CRISPR/Cas9 editing of endogenous banana streak virus in the B genome of Musa spp. overcomes a major challenge in banana breeding. Comm Biol. 2019.

Food Deserts: a Problem of Supply or Demand?

That poor people have a less healthy diet than rich people is not in doubt. That poor people have worse health because they have less healthy diets is also not in doubt. That poor people have less access to healthy food than rich people is, again, not in doubt. This series of observations has led to a predominant narrative: that the poor are denied the healthy foods that they would choose, where it only that they had equitable access to healthy options.

This does not follow, any more than the argument that low access to contraception is causative of high birth-rates. It is quite feasible that low demand is the cause of both low access and the corresponding outcomes, both in the case of the pill and low access to healthy food.

Allcott and colleagues addressed this issue with respect to diet and health.[1] They examined the possibility that observed differences in supply of healthy foods are a response to differences in the demand for those foods in different neighbourhoods. The authors examined this through a rich array of data sets, one of which covered nearly half of all US grocery purchases. They were able to examine how people of different socioeconomic group behave when supermarkets are established in new locations, or when people move into, or out of, food ‘deserts’. Effectively they treat these geographic changes as instrumental variables.

When they examined the effect of entry of a new supermarket in a given locality, they find that local supermarket entry does not materially increase healthy eating. Then they examined the converse – movement of a household to an environment where more healthy food is available. Again, behaviour does not converge towards the general eating pattern in the new location.

Could this be because the supermarkets charge more for healthy products in poor neighbourhoods than they do in rich neighbourhoods? The authors examined this possibility and were able to exclude it. What they found is that poorer households are willing to pay much less than wealthier households for healthy food. As a result they are provided with less healthy food.

The results are broadly consistent with studies on education and food preferences. Food deserts exist, but they are not the result of supply-side failure. Rather they reflect the role of culture and tastes in the United States, as they have been shown to do in so many other places. The effects observed in the study did not change over many years. Policy initiatives that simplistically target food deserts are thus unlikely to succeed.

— Richard Lilford, CLAHRC WM Director

Reference:

1. Allcott H, Diamond R, Dubé J-P. The Geography of Poverty and Nutrition: Food Deserts and Food Choices Across the United States. NBER Working Paper No. 24094. 2018.

Improving Access to Fresh Food in Low-Income Areas

In a previous News Blog we looked at a paper that found an association between adherence to the Mediterranean diet (i.e. high consumption of fruit, vegetables, and legumes) and reduction in cardiovascular disease risk.[1] So, it can be argued, that for those in low-income areas there is a need to improve their access to fresh fruit and vegetables. But how best to achieve this? Breck and colleagues, on behalf of the CDC, looked at one possibility in a cross-sectional survey analysis.[2]

Previously, the city of New York had attempted to address the issue by granting new licenses for mobile fruit and vegetable carts in those neighbourhoods with poor availability of fresh food. However, only some of the carts (27%) had the capacity to accept the Supplemental Nutrition Assistance Program (SNAP) benefits (a federal aid program to provide food-purchasing assistance) through use of Electronic Benefit Transfer (EBT) machines.

The authors conducted a survey analysis of 779 adults shopping at four carts in the Bronx neighbourhood of New York over several time periods. After controlling for cofounders, they found that those shoppers who were able to pay using their SNAP benefits purchased significantly (p<0.001) more fruit and vegetables (an average of 5.4 more cup equivalents), than those who were only able to pay with cash. While there are promising results from providing consumers with more ways to pay, there are challenges that could prevent widespread roll out of EBT, chiefly the high initial, monthly, and transaction fees that the cart vendors need to pay. Even when provided with financial support, less than one-third of carts were equipped with EBT machines at the time of this study. Although the study has a number of limitations that means causal inferences cannot be drawn, it can be seen as a possible avenue for future research.

— Peter Chilton, Research Fellow

Reference:

1. Chilton P. Diet and Socioeconomic Status. 18 August 2017.
2. Breck A, Kiszko K, Martinez O, Abrams C, Elbel B. Could EBT Machines Increase Fruit and Vegetable Purchases at New York City Green Carts? Prev Chronic Dis. 2017; 170104.

Stop Being Beastly to Malthus!

I never understand why people think that Malthus got it so badly wrong. His argument (the Malthusian trap) was that resources are finite and that, therefore, there must be some limit to the number of people that the world can feed.[1] While it certainly turned out that the world can feed many more people than he thought, this does not disprove the underlying theorem. At some point there must come a threshold, where food supply really fails to meet the demand. If we generalise from food to include water, then that point might not be as far away as complacent people think. Of course, we also have to take into account the environmental damage associated with feeding, transporting, and keeping a large number of people warm.

Malthus has become almost a figure of derision. While he may have been wrong about when, the jury is still out about whether. He was right about the generic point, that there is a limit to the carrying capacity of our planet. Food is central to this, because even if we do not run out of food, much environmental damage is caused in its production.

The world’s population will stabilise in about 50 years, although African populations will continue to expand for a while longer.[2] So we should mitigate the environmental effects of food production. I like to eat beef from time to time. However the production of beef is very energy intensive and the methane released by cattle contributes about 20% of the total global warming.[3] So I favour a tax on all beef, similar to that on fuel. Such a tax is more justifiable even, then a tax on sugar and tobacco. This is because consumption of sugar and tobacco does not have the strong externalities associated with fossil fuels and production of beef. There is no proper libertarian argument against taxation in circumstances where strong externalities apply.[4] Pigovian taxes are taxes designed to compensate for externalities and to reduce behaviour that harms others; they would seem entirely justified in this case. I am less of a fan of Pigovian taxes to deal with internalities – that is to stop people from harming themselves. But as it turns out, red meat is bad for our health, as discussed in a recent news blog.[5]

So let us give Malthus his due. He might have got the detail wrong, but his principle still stands. I vote for the rehabilitation of Malthus.

— Richard Lilford, CLAHRC WM Director

References:

1. Malthus TR. An Essay on the Principle of Population. London, UK: J. Johnson, 1798.
2. Lilford RJ. The Population of the World – Will Depend on What Happens in Africa. NIHR CLAHRC West Midlands News Blog. 9 January 2015.
3. Steinfeld H, Gerber P, Wassenaar T, Castel V, Rosales M, de Hann C. Livestock’s Long Shadow: Environmental Issues and Options. Rome, Italy: Food and Agriculture Organization, 2006.
4. Lilford RJ. An Issue of BMJ with Multiple Studies on Diet. NIHR CLAHRC West Midlands News Blog. 4 August 2017.
5. Capewell S, Lilford R. Are nanny states healthier states? BMJ. 2016; 355: i6341.

How Much Fruit and Veg is Enough?

We are often told that we should be eating five (or is it now ten?) portions of fruit and vegetables each day to protect against, amongst other things, cardiovascular disease (CVD).[1] However, such recommendations are generally based on research conducted in people from Europe, the USA, Japan and China. There is little data from countries in the Middle East, South America, Africa or South Asia.

The PURE study (Prospective Urban Rural Epidemiology) set out to rectify this, recruiting 135,000 participants from 18 countries, ranging from high-income countries, such as Sweden, to low-income countries, such as India.[2] The research team documented the diet of these individuals at baseline (using questionnaires specific to each country), then followed them up for a median of 7.4 years, looking at cardiovascular-related clinical outcomes. As expected higher intakes of fruit, vegetables and legumes were associated with lower incidences of major CVD, myocardial infarction, and mortality (cardiovascular-related and all-cause). However, the hazard ratio for all-cause mortality was lowest for three to four servings (375-400g) per day (0.78, 95%CI 0.69-0.88), with no significant decrease with higher consumption.

It is more likely that consuming around 375g of fruit/vegetables/legumes per day will be within the financial reach of people living in poorer countries, compared to the various recommendations of 400-800g that are often seen in Europe and North America. Before we ditch that extra snack of carrot sticks, however, it is important to note that factors such as food type, nutritional quality, cultivation and preparation are likely to vary between countries, while other clinical outcomes, such as cancer, were not looked at in this study.

The authors are continuing to enrol more participants, and are hoping to re-examine their results in the future.

— Peter Chilton, Research Fellow

References:

1. Oyebode O, Gordon-Dseagu V, Walker A, Mindell JS. Fruit and vegetable consumption and all-cause, cancer and CVD mortality: analysis of Health Survey for England data. J Epidemiol Community Health. 2014; 68(9): 856-62.
2. Miller V, Mente A, Dehghen M, et al. Fruit, vegetable, and legume intake, and cardiovascular disease and deaths in 18 countries (PURE): a prospective cohort study. Lancet. 2017.

An Issue of BMJ with Multiple Studies on Diet

This News Blog often contains information about diet and health. For example, we have cited evidence that salt is enemy number one [1]; trans-fats are unremittingly bad news [2]; and large amounts of sugar are harmful.[3] After that the risks become really rather small – relative risks of about 20%. Fruit, and more especially vegetables, are good news. Milk is an unhealthy drink in adults (never intended for that purpose and galactose is harmful, unless removed during a fermentation process).[4] Three further studies of diet were included in a single recent issue of the BMJ.[5-7]

The first study by Etemadi, et al. looked at meat consumption in a large cohort of people (n= 536,969) who gave detailed dietary histories.[5] The evidence corroborates other studies in showing that red meat is harmful, increasing relative risk of death by about 20% in high meat eaters compared to moderate meat eaters. The difference is greater if the comparison is made with people who obtain almost all of their meat in the form of fish and chicken. The causes of death that showed greatest increases in risk with high red meat consumption were cancer, respiratory disease and liver disease. Surprisingly, perhaps, increased risk from stroke was nugatory. The increased risk in unprocessed meat is probably related to haem iron, and in processed meat to nitrates/nitrites – there are all pro-oxidant chemicals. Of course this is an association study, so some uncertainty remains. The main problem with meat, as the BMJ Editor points out,[8] is the harmful environmental effects; apparently animal husbandry contributes more to global warming than burning fossil fuels. I take the environmental effects seriously – perhaps we will one day vilify meat farmers more vociferously than we currently vilify tobacco farmers. After all, individuals don’t have to smoke, but cannot protect themselves from the harmful effects of pollution.

Meanwhile, for those who are interested, the other two relevant articles in this issue of the BMJ looked at avoiding gluten in people who do not have celiac disease (no benefit and evidence points towards harm),[6] and the beneficial effect of a low salt and fat diet on gout.[7]

— Richard Lilford, CLAHRC WM Director

References:

1. Lilford RJ. Effects of Salt in Diet. NIHR CLAHRC West Midlands News Blog. 17 October 2014.
2. Lilford RJ. On Diet Again. NIHR CLAHRC West Midlands News Blog. 23 October 2015.
3. Lilford RJ. How Much Sugar is Too Much? NIHR CLAHRC West Midlands News Blog. 25 September 2015.
4. Lilford RJ. Two Provocative Papers on Diet and Health. NIHR CLAHRC West Midlands News Blog. 12 December 2014.
5. Etemadi A, Sinha R, Ward MH, Graubard BI, Inoue-Choi M, Dawsey SM, Abnet CC. Mortality from different causes associated with meat, heme iron, nitrates, and nitrites in the NIH-AARP Diet and Health Study: population based cohort study. BMJ. 2017; 357: j1957.
6. Lebwohl B, Cao Y, Zong G, Hu FB, Green PHR, Neugut AI, Rimm EB, Sampson L, Dougherty LW, Giovannucci E, Willett WC, Sun Q, Chan AT. Long term gluten consumption in adults without celiac disease and risk of coronary heart disease: prospective cohort study. BMJ. 2017; 357: j1892.
7. Rai SK, Fung TT. Lu N, Keller SF, Curhan GC, Choi HK. The Dietary Approaches to Stop Hypertension (DASH) diet, Western diet and risk of gout in men: prospective cohort study. BMJ. 2017; 357: j1794.
8. Godlee F. Red meat: another inconvenient truth. BMJ. 2017; 357: j2278.

Fine Dining and Fine Hygiene are Negatively Correlated

A recent study shows that restaurants rated highly in food guides are associated with a greater overall risk of foodborne gastrointestinal diseases outbreaks than your run-of-the-mill restaurant.[1] However, the ‘high-end’ restaurants also score more highly on the Food Agency Inspection visits. So why do the posh restaurants generate more GI diseases than their more mundane peers despite better hygiene in the restaurants with the best food? The high disease risk in highly rated restaurants probably comes from the nature of the food served (e.g. oysters) and cooking methods (e.g. low temperatures to produce chicken liver parfait). So the risk is real, but worth running!

— Richard Lilford, CLAHRC WM Director

Reference:

1. Kanagarajah S, Mook P, Crook P, Awofisayo-Okuyelu A, McCarthy N. Taste and Safety: Is the Exceptional Cuisine Offered by High End Restaurants Paralleled by High Standards of Food Safety? PLoS Curr Outbreaks. 2016.