This week I cover health effects of coffee and caffeine consumption, diet assessments in clinical practice, fruit and vegetable consumption for liver health and ways to influence diet choice to reduce meat consumption.

DIET AND CARDIOVASCULAR HEALTH: We know that diet choices have a direct impact on the risk of cardiovascular disease (CVD). A paper published in 2019 using data from the Global Burden of disease study analysed dietary risk factors in 51 countries in the WHO European region associated with the risk of death from CVD. The results showed that in 2016, dietary risk factors were associated with 2.1 million CVD deaths accounting for 22.4% of all deaths and 49.2% of CVD deaths. Regarding individual dietary risk factors, a diet low in wholegrains accounted for approximately 429,000 deaths, followed by a diet low in nuts and seeds (341,000 deaths), a diet low in fruits (262,000 deaths), a diet high in sodium (251,000 deaths), and a diet low in omega-3 fatty acids (227,000 deaths). The study predicted that if everyone adopted a healthy diet, 1 in 5 premature deaths could be prevented. With this in mind, the 2019 guidelines from the American College of Cardiology for primary prevention of CVD recommend a plant-based eating plan — ‘Plant-based and Mediterranean diets, along with increased fruit, nut, vegetable, legume, and lean vegetable or animal protein (preferably fish) consumption…’,. The necessity of fish consumption for omega-3 fats continues to be a topic of debate and I have shared my viewpoint here. We also know that healthy vegetarian and vegan diets have been associated with a much lower risk of CVD than other common diet patterns.

The paper highlighted is a statement from the American Heart Association making a case for the adoption of diet assessment tools by doctors and other healthcare professionals as a routine part of clinical care. Examples of rapid diet screening tools are provided from the 2 question Nutrition Screening Protocol to the more extensive Mediterranean Diet Adherence Screener. Given the extent to which unhealthy diets contribute to the burden of CVD, healthcare professionals can no longer ignore their patients diet. This statement is a significant step forward in getting diet assessment incorporated into routine clinical practice. As many in the lifestyle medicine movement are already advocating, diet should be considered a ‘vital sign’ along with height, weight, blood pressure and such like. However, the real challenge comes with helping patients to change longstanding dietary behaviours, which we know are dependent on so many intrinsic and extrinsic factors.

IS DRINKING COFFEE HEALTHY?: There are strong opinions on both sides of this debate. This review summarises the scientific data on coffee consumption and health, specifically with regards to its caffeine content. In addition to caffeine, coffee contains hundreds of phytochemicals and polyphenols that form during roasting. It also has magnesium, potassium, and niacin (vitamin B), which all help reduce oxidative stress, improve your gut microbiome, and regulate fat metabolism. Data relating to health outcomes are predominantly from prospective cohort studies in which healthy populations are followed over time. Concerns have been raised about an increased risk of cancer as cooking coffee beans at high temperatures forms the carcinogen acrylamide. However, there are no studies that show acrylamide in coffee increases the risk of cancer. In fact coffee consumption is strongly associated with a reduced risk of endometrial and liver cancer and a slightly reduced risk of melanoma, mouth and throat cancer, breast cancer, and prostate cancer. Coffee consumption may reduce insulin resistance in the liver and has been associated with a reduced risk of type 2 diaebtes. Coffee consumption also reduces the risk of Parkinson disease, gallstones and possibly kidney stones. 2–5 cups a day is associated with a reduced risk of death from any cause. Of note, unfiltered coffee consumption is associated with elevated cholesterol and LDL-cholesterol levels due to the higher levels of the compound cafestol. Of course, for some individuals coffee/caffeine consumption may result in unpleasant side effects such as insomnia, anxiety and tremor. If this is you, then probably best not to drink coffee. For everyone else, coffee consumption can be part of a healthy diet and 3–5 standard cups of coffee per day (8 fluid ounces, 90mg of caffeine) is perfectly safe and may be associated with health benefits.

CAFFEINE IN PREGNANCY: This review provides a warning against coffee consumption during pregnancy. Pregnancy greatly reduces caffeine metabolism, especially in the third trimester, when the half-life can be up to 15 hours rather than the usual 2.5–4.5 hours. Newborns have a limited capacity to metabolise caffeine, and the half-life is about 80 hours. Caffeine readily crosses the placenta and the slow metabolism in the foetus can result in high circulating levels. The author of this paper reviewed 37 observational studies and 17 meta-analyses and concludes that caffeine is associated with an increased risk for miscarriage, stillbirth, low birth weight and/or small size for gestational age, and childhood acute leukemia. The studies reviewed showed a dose-response relationship as well as no minimum threshold for safety. The author suggests that the data supports complete avoidance of caffeine during pregnancy.

Of course, many of us habitually consume coffee and there may be issues with withdrawal if stopped suddenly. Symptoms of caffeine withdrawal include, headaches, fatigue, decreased alertness, and depressed mood, as well as influenza-like symptoms in some cases. These symptoms typically peak 1 to 2 days after cessation of caffeine intake, with a total duration of 2 to 9 days, and can be reduced by gradually decreasing the caffeine dose. Preconception advice should be tailored to include gradual caffeine withdrawal prior to pregnancy.

DIET AND NON-ALCOHOLIC FATTY LIVER DISEASE (NAFLD): Diet is a major contributor to the growing burden of NAFLD globally, with the prevalence in Western countries as high as 20% in adults. The main risk factors are diets high in saturated fat, processed foods and fructose, in part due to associations with overweight and obesity and metabolic syndrome. Vegetarian diets and plant-based diets in general have been associated with a reduced risk of NAFLD and may play a role in its treatment. The study highlighted examined the association of fruit and vegetable consumption in 52 280 participants from the Health Examinees study cohort in Korea and the risk of NAFLD, with a median follow up of 4.2 years. The results showed that higher intakes of fruits and vegetables reduced the risk of NAFLD in the order of 20–30%. Higher intakes in this population were around 300–400g of fruit (approx 5 portions) and 180–200g of vegetables (approx 2–3 portions) per day.

There is often confusion around the association between fructose consumption and risk of NAFLD versus the conusmption of frutose in fruit. Fruit consumption is entirely different from consuming free fructose in the form of table sugar or high fructose corn syrup. Table sugar, or sucrose, is made up of equal parts of glucose and fructose. This free fructose can for the most part only be metabolised in the liver and it gets converted to triglycerides and uric acid. These triglycerides, when in excess, get stores in the liver cells contributing to fatty liver. The uric acid can contribute to the risk of developing kidney stones and gout and also inhibits nitric oxide production in blood vessels. However, fructose when consumed in fruits and vegetables is accompanied by fibre and a large array of vitamins, minerals and antioxidants and is not associated with adverse effects on the liver. In fact, fruit and vegetable consumption is associated with a reduced risk of a number of chronic diseases and a reduced risk of death from all cause, with around 10 portions a day being optimal. A note of caution, excess consumption of fruit juice may not be so healthy although in this current study apple juice consumption was associated with lower risk of NAFLD.

SUSTAINABLE DIETS; HOW ARE WE DOING?: Our diet choice is no longer just a matter for personal health. The global food system is a major contributor to climate change with animal agriculture being particularly harmful due to its contribution to greenhouse gas emissions, land use change, loss of biodiversity, species loss, water pollution etc. Livestock farming and aquaculture is responsible for around 58% of the greenhouse gas created by global food, and takes up 80% of farmland despite contributing just 18% of the world’s calorie intake. A shift to a plant-based food system is accepted as necessary to meet the Paris Agreement and Sustainable Development Goals. So how are we doing? Sadly not well at all. This stark report from the Eat Forum highlights the lack of progress since the publication of the Eat-Lancet commision report on healthy, sustainable diets in January 2019. The current report focuses on the G20 countries and concludes that dietary habits in these countries are destroying the planet. If the whole world ate in this way we would need the resources of 7 planets to feed the global population. If these countries continue to eat in such a way then we will not be able to keep global warming below 1.5°C. Food related green house gas emissions need to be cut in half by 2050 to keep us within planetary boundaries. The good news is that what is good for the planet is also good for our health. Centring our diet around fruits, vegetables, wholegrains, legumes, nuts and seeds whilst reducing drastically or eliminating animal-derived foods will improve personal health and help heal the planet for future generations.

HOW DO WE CHANGE DIETARY HABITS?: This is the hard part. On the basis of this report, it seems we can be nudged into making better choices even if these decisions may not be conscious ones. An experiment at Cambridge University found that when the same price meat and vegetarian options were placed side by side in the student canteen, meat-based meals were more frequently chosen. However, if meat-based meals were placed more than 187cm further away from the vegetarian meals, the latter were more likely to be chosen with 25% of students choosing the vegetarain meals compared to the usual 17%. A previous study from the same group showed that increasing plant-based options results in more people choosing a vegetarian meal. These data confirm the importance of the food environment and when plant-based options are accessible and affordable, people are more likely to make the better choice.

VITAMIN D SUPPLEMENTATION: Vitamin D has come into the spotlight in recent months given the potential link between lower blood levels and worse outcomes from COVID-19. With lockdown measures further reducing exposure to sunlight (the main source of vitamin D), Public Health England has recommended all citizens in the UK continue taking vitamin D supplements beyond the usual recommendations for the winter months. However, the dose of vitamin D recommended by different health organisaitons around the world varies as does the optimal level to aim for in serum. In addition, poeople living with obesity require a 2–3 x increased dose given that vitamin D is fat soluble. It seems experts are now recommending that optimal serum levels are between 100–150 nmol/l. The authors state ‘Three lines of evidence converge on the optimal serum 25(OH)D at 120 nmol/L. This is the blood level that would naturally occur with regular sun exposure, levels at which the body’s compensation mechanism for low levels is turned off, and levels at which mom has enough vitamin D for it to be in her breast milk (vitamin D is the only supplement recommended from birth).’

On review of the evidence, the authors of this review recommend the best way to establish the optimal supplementary dose is to tailor it to the specific individual by measuring serum 25(OH) vitamin D and adjusting vitamin D dose accordingly to achieve 25(OH)D levels of 75–250 nmol/L. A guide is provided in the table below from the paper. Vitamin D3 is the preferred form for supplementation.

The baseline serum level dose not alter the above recommendations but the authors recommend re-testing serum levels after 3–6 months of supplementation. For every 100 IU/d ingested the circulating levels of 25(OH) vitamin D will increase and maintained at about 1.5–2.5 nmol/L after 8–12 weeks. Therefore, healthy normal weight adults ingesting 2000 IU/d can expect to maintain a circulating level of 25(OH) vitamin D in the range of 75–100 nmol/L. Those who take 5000 IU/d can raise and maintain their blood levels in the range of 100–150 nmol/L. Vitamin D toxicity is extremely rare.

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