35th World Vegetarian Congress
'Food for all our futures'
Heriot Watt University, Edinburgh, Scotland
July 8-14, 2002

by Stephen Walsh, PhD

[ Vai alla traduzione in italiano ]

  • Vegetarian health and mortality
  • Avoiding obesity and diabetes
  • Cardiovascular health
  • Bone health
  • Preventing cancer
  • Clear mind and clear vision
  • Steady metabolism
  • The pros and cons of fish and dairy
  • Recommendations

Vegetarian health and mortality

All major studies of vegetarians have found vegetarians to live about 5 years longer than the general population in their country and to have good general health.

Much of this advantage lies in less smoking, more exercise and characteristics of diet other than just avoiding meat.

Heavy smoking can take a decade from your life and lack of exercise can take away 2-3 years even if not resulting in excess weight.

We need to learn from studies of vegetarians and others about dietary choices promoting health:

  • daily consumption of nuts can add two years to your life (more for men)
  • obesity can cost about 2.5 years of life in women and 4 years in men
  • fruit and vegetables can reduce risk of cancer, heart disease and other illnesses
  • elevated homocysteine may cost about 4 years in life and may be especially dangerous for diabetics
  • blood pressure and risk of stroke and osteoporosis can be lowered by a diet rich in potassium and calcium and low in sodium

Avoiding obesity and diabetes

Obesity (BMI >30) is a primary cause of diabetes through promoting insulin resistance. Increased BMI also reduces HDL (good) cholesterol, and increases LDL (bad) cholesterol and blood pressure and risk of heart disease, colon cancer and breast cancer. Overall obesity costs about 3 years in life expectancy.

The ideal BMI is 20-23 for most people. For a 1.83 m (6') person this translates to 67-77 kg (10 st 7 lb to 12 st)

Risk of obesity is reduced by diets high in fibre and low in calorie density: plenty of fruit and vegetables. Sugary drinks promote obesity; snacking on fruit and vegetables reduces obesity.

High physical activity, low saturated fat intake and high fibre intake reduce the risk of diabetes whether obese or not.

Low chromium or magnesium intake may increase risk of diabetes. Plenty of fruit and vegetables and whole grains instead of refined grains will avoid this increase in risk.

Western vegetarians show relatively low levels of obesity and diabetes compared with nonvegetarians.

Cardiovascular Health

The magic combination is low LDL cholesterol, high HDL cholesterol, low blood pressure, high omega-3 fatty acids, high total antioxidant capacity and low homocysteine.

A low intake of saturated and trans (hydrogenated) fat and a moderate intake of unsaturated fat promotes a good cholesterol balance, as do BMIs in the low 20s and physical activity.

Low blood pressure is promoted by low sodium intake and high potassium and calcium intakes, and by low BMI.

Omega-3 fatty acids can be readily obtained from flaxseed (culinary grade linseed), hempseed, rapeseed (canola) and walnuts.

Homocysteine is reduced by adequate B vitamins (particularly B12, folate, B2 and B6) and by avoiding coffee and smoking.

Vegetarians of all types show reduced risk of heart disease, but more attention to increasing B12, omega-3 fats and calcium intakes and to reducing trans fats and salt could give substantial further improvements.

Diet and blood pressure
High sodium
(3.5 g)		 Medium sodium
(2.4 g)		 Low sodium
(1.3 g)
Control 133/83 131/82 126/79
DASH 127/80 126/79 124/78

DASH= Dietary Approaches to Stop Hypertension

Potassium Calcium Fibre Saturated fat
Control 1700 mg 450 mg 10 g 14%
DASH 4400 mg 1250 mg 30 g 7%

Other studies indicate that slightly over half the benefit of DASH derives from potassium and most of the rest from calcium.

Increased calcium, potassium and magnesium intakes are all associated with reduced stroke mortality.

Reduced blood pressure is associated with reduced mortality from all causes.

Vegetarians are often (but not always) found to have lower blood pressure.

Bone health

At any age a fracture is inconvenient, but a hip fracture can be particularly immobilising with adverse effects on quality of life.

The keys to bone health are

  • making it easy to match calcium losses with dietary calcium absorption
  • making it difficult to lose calcium from the bones

The key to the former is the same triad as for blood pressure: low sodium, high potassium and high calcium. If sun exposure is limited, e.g. during winter at latitudes above 40, dietary vitamin D becomes important.

Protein has a U-shaped effect: beneficial up to about 1g per day per kilogram of body weight by promoting bone growth, adverse thereafter through increasing calcium losses.

The most effective way to keep calcium in the bones is to ensure adequate vitamin K from green leafy vegetables or broccoli. A serving a day can reduce fracture risk by 50%.

Retinol from supplements or from fortified low-fat milks in the USA and Sweden probably promotes bone loss.

Results on vegetarian bone health are still unclear.

Effect of different foods on calcium balance
(mg calcium per 100 g of food)
Normal absorption 40% reduced absorption
Chicken (average) -27.3 -27.8
Fish (average) -23.6 -24.9
Eggs -18.2 -20.7
Cottage cheese -15.6 -18.0
Cheddar cheese 18.6 -3.7
Cow's milk 8.5 3.8
Fortified soy milk 7.6 4.0
Wheat grain (dry) -11.6 -12.8
Almonds 14.8 5.0
Soy beans 6.6 -1.6
Potatoes 1.8 1.3
Peppers 2.6 2.2
Oranges 5.6 4.0
Bananas 4.6 4.4
Kale 17.6 11.7
Spring greens 20.7 12.4

The best foods for bone health are low oxalate leafy greens as they reduce calcium losses, provide readily absorbed calcium and provide the vitamin K to keep calcium in bones where it belongs. Dairy products are not even as effective as a simple calcium carbonate supplement let alone leafy greens.

Preventing cancer

Obesity promotes postmenopausal breast cancer, endometrial cancer, colorectal cancer and kidney cancer.

Evidence for an overall benefit for fruit and vegetables has declined over the past five years as more prospective studies have reported.

Evidence for benefit now centres on folate (greens and beans) and carotenoids, particularly lycopene (brightly coloured vegetables, particularly red) and possibly fibre.

There is modest evidence for a benefit of calcium and vitamin D on colorectal cancer and breast cancer and for vitamin D and selenium on prostate cancer.

The evidence for an adverse effect of cow's milk on prostate cancer and an adverse effect of preserved meat on colorectal cancer is reasonably strong.

Foods and drinks consumed when very hot increase risk of mouth and throat cancer.

There is very little evidence for an effect of fat intake on cancer risk, except via increased weight.

Clear mind and eyes

Poor cardiovascular health and oxidative stress promote dementia and cognitive decline. Oxidative stress is a major factor in macular degeneration and cataracts.

Elevated homocysteine is strongly associated with dementia (both vascular dementia and Alzheimer's disease).

Green leafy vegetables including spinach, kale and broccoli are antioxidant powerhouses as well as providing folate to reduce homocysteine and the particular carotenoids that protect eyes from oxidative damage.

B12 (along with folate) is key to low homocysteine levels in vegetarians.

Brightly coloured vegetables and fruits are the best source of antioxidants (kale, spinach, tomatoes, carrots, blueberries, strawberries and plums are all excellent sources).

Nuts and seeds and olives are also useful sources.

Brazil nuts are an exceptionally concentrated source of selenium (one a day is enough).

Steady metabolism

The pacemaker of metabolism is the thyroid gland, which thrives on adequate but not excessive amounts of iodine.

The ideal intake range is about 150 to 400 micrograms per day.

Iodised salt is not an ideal source due to the accompanying sodium.

In the UK iodine intake is boosted by adding iodine to cattle feed: a very roundabout method of making up for low soil levels of iodine.

Seaweeds contain anything between 5 and 5000 micrograms of iodine per gram, with kelp (kombu) having the highest and most consistent content.

15 grams of kelp per year is enough to provide all the iodine needed. A kilogram of nori provides a more variable but smaller amount of iodine than 15 grams of kelp. If taking kelp tablets take no more than 500 mg of kelp per week (do not rely on the stated iodine content).

Selenium supports thyroid function as well as being and important antioxidant and can be readily boosted by a Brazil nut a day.

Pros and cons of fish

Large trials on fish and fish-oils in heart attack survivors show mortality reductions of between 15% and 30%.

Trials using plant-centred diets incorporating vegetable oils high in monounsaturated and omega-3 fatty acids show mortality reductions of 50-70% - a much better result.

Studies of fish consumption in Finland, with high mercury contamination of inland fish, show increased mortality with increased fish consumption.

Fish consumption in the modern world is neither necessary nor safe nor sustainable.

Omega-3 fats can be readily obtained from rapeseed oil, flaxseed, walnuts and green vegetables.

One teaspoon of flaxseed oil or one tablespoon of ground flaxseed or two tablespoons of rapeseed oil provides an adequate daily intake.

Pros and cons of dairy

Dairy products are a rich source of calcium, vitamin B12 and (depending on cattle feed) iodine, but they are an even richer source of unwanted saturated fat.

Swapping butter and cream for rapeseed (canola) margarine and olive oil was one of the key changes in the Lyon Diet Heart Trial (70% reduction in mortality).

The Nurses study results indicated that swapping 5% of calories from saturated fat to 5% of calories from unsaturated fat would reduce heart disease by 40%.

Low fat dairy products protect individuals, but not communities: once the cow has been milked the fat is in the food supply and someone will end up eating it.

Contrary to propaganda, dairy foods range from being moderately beneficial to bone health to having notable adverse effects. There are better alternatives.

Simply dropping dairy products will not promote health but dropping dairy products and getting adequate calcium, B12 and iodine from other sources, while avoiding the health risks of saturated fat, will strongly promote health.

Lessons from primate diets (I)

Human studies mostly point towards plant foods, including vegetables, fruits and nuts, as the basis for long term health.

However, getting ideal amounts of vitamin B12, and to a lesser extent calcium and omega-3 fatty acids, from a purely plant-based diet is no trivial matter.

Research on the diets of primates sheds an interesting light on why this is so.

All primates consume insects and dirt either deliberately or incidentally and this provides an important source of B12 missing in hygienic plant-based diets.

The wild fruits eaten by many primates are rich in minerals and have about 10 times the calcium content of modern cultivated fruits. Grains are also low in calcium compared to plant foods eaten by other primates. Plant omega-3s are low in cultivated fruit and grains, but high in typical wild plants eaten by monkeys.

Daily intakes of a howler monkey
Calcium Magnesium Potassium Sodium Iron
4500 mg 1300 mg 6400 mg 180 mg 40 mg
Omega-6 Omega-3 Saturated Total fat Vitamin C
4% 3% 8% 17% 600 mg

Lessons from primate diets (II)

Larger primates such as chimpanzees and gorillas also have very high mineral intakes by human standards.

Captive primates are fed diets with at least 500 mg of calcium per 100 g of food by dry weight.

This is equivalent to about 3000 mg per day for a human adult. Estimated palaeolithic human intake of calcium (almost all from plants) is about 1500 mg per day.

The nutritional weak points of plant-based diets do not exist in typical primate diets which are very rich in minerals, including calcium, and include adequate amounts of vitamin B12 from insects and dirt.

In contrast to fruits, cultivated green leafy vegetables have a similar calcium content to the wild leaves eaten by other primates. This gives them a special importance in modern plant-based diets. If greens are not consumed in large amounts (e.g. 200 g of kale or 500 g of dark lettuce per day) then 500 mg of calcium from fortified foods or supplements is indicated.

Some particular nuts and seeds (flax, hemp, walnuts) are particularly high in omega-3 fatty acids and are therefore useful to balance grains and fruits.

Recommendations

Eat plenty of brightly coloured vegetables and fruits including some green leafy vegetables or broccoli.

Eat a moderate amount of nuts and seeds, particularly almonds, peanuts, cashews, hazels (filberts), walnuts and flaxseed and a small amount of Brazil nuts.

Use healthy monounsaturated oils and fats such as olive, avocado, rapeseed (canola) and peanut (groundnut) oil.

Make whole grains and fruit the main starchy foods.

Limit salt intake (get iodine from somewhere else if currently using iodised salt)

Avoid supplements with vitamin A or beta carotene and use kelp tablets no more than twice a week.

Make sure you get at least 3 micrograms of vitamin B12 per day from either vitamin B12 fortified foods or a B12 supplement.

Ensure an adequate calcium and vitamin D intake.

References

Fraser (2001): Archives of Internal Medicine, 2001; 161: 1645-1652, Gary Fraser, Ten years of life: Is it a matter of choice.

Key et al. (1999): American Journal of Clinical Nutrition, 1999; 70: 516S-524S, Timothy J Key et al., Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies

Appleby et al. (2002), Public Health Nutrition, 2002; 51: 29-36, Paul N Appleby et al., Mortality in British vegetarians

Appleby et al. (1999), American Journal of Clinical Nutrition, 1999; 70: 525S-531S, Paul N Appleby et al., The Oxford Vegetarian Study: an overview

Mann et al. (1997): Heart, 1997; 78: 450-455, Jim I Mann et al., Dietary determinants of ischaemic heart disease in health conscious individuals

Stevens (2000): Nutrition Reviews, 2000; 58: 129-137, June Stevens, Impact of age on associations between weight and mortality

Khaw et al (2001): The Lancet, 2001; 357: 657-663, Kay-Tee Khaw et al., Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study: a prospective population study

Kohlmeier et al. (1997), American Journal of Epidemiology, 1997; 146: 618-626, Lenore Kohlmeier et al., Lycopene and myocardial infarction risk in the EURAMIC study.

Kark et al. (1999): Annals of Internal Medicine, 1999; 131:321-330, Jeremy D Kark et al., Nonfasting plasma total homocysteine level and mortality in middle-aged and elderly men and women in Jerusalem

Vollset et al. (2001): American Journal of Clinical Nutrition, 2001; 74: 130-136, Stein Emil Vollset et al., Plasma total homocysteine and cardiovascular and noncardiovascular mortality: the Hordaland Homocysteine Study

Bostom et al. (1999): Archives of Internal Medicine, 1999; 15: 1077-1080, Andrew G Bostom et al., Nonfasting plasma total homocysteine levels and all-cause and cardiovascular disease mortality in elderly Framingham men and women

Hoogeveen et al. (2000): Circulation, 2000; 101: 1506-1511, Ellen K Hoogeveen et al., Hyperhomocysteinemia increases risk of death, especially in Type 2 diabetes

Sacks et al. (2001): New England Journal of Medicine, 2001; 344: 3-10, Frank M Sacks et al., Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet

Halvorsen et al. (2002), Journal of Nutrition, 2001; 132: 461-471, Bente L Halvorsen et al., A systematic screening of total antioxidants in dietary plants

Milton (1999): Nutrition, 1999; 15: 488-498, Katherine M Milton, Nutritional characteristics of wild primate foods: Do the diets of our closest living relatives have lessons for us?

Eaton et al. (1987), New England Journal of Medicine, 1987; 312: 283-289, S. Boyd Eaton and Melvin Konner, Paleolithic Nutrition: a consideration of its nature and current implications.

Further information and references can be found in

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Published Online: 28 Aug 2002