Transcript Document

Impact on health of food
interventions
Kirsten Brandt
Human Nutrition Research Centre
Research Group Food Quality & Health
Newcastle University
www.ncl.ac.uk/afrd
Impact on health of food
interventions
• Observational studies and intervention studies
– Assessment of effects of foods and diets
– Assessment of effects of individual nutrients
• Examples of intervention studies with plant foods
– Intervention studies with wholegrain foods (WHOLEheart,
GrainMark)
– Intervention study with fruit (Fruit at Work)
– Intervention study with vegetables (VegBP)
• Importance for public policy and the horticultural industry
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Observational studies and
intervention studies
• Assessment of effects of foods and diets using
observational studies
– Method: Record the diets for volunteers, and record the
occurrence of diseases and/or risk indicators.
– Advantages: Cheap and relatively rapid, allows large numbers of
people, results relevant for real diets.
– Disadvantages: Difficult to control for confounding factors,
systematic weaknesses in methods for assessing diets.
• Conclusion: Important tool for development of hypotheses,
but cannot provide a definitive proof.
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Observational studies and
intervention studies
• Assessment of effects of foods and diets using
intervention studies
– Method: Randomly assign volunteers to follow different diets, then
record changes in diseases and/or risk indicators.
– Advantages: Can in principle eliminate the confounding factors.
– Disadvantages: Very expensive and difficult, placebo difficult or
impossible, only possible for relatively short term effects.
• Conclusion: Essential to either verify or disprove outcomes
of observational studies.
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Observational studies and
intervention studies
• Assessment of effects of individual nutrients
– Observational: Assess diets and then calculate intake of each
nutrient, to compare with health data.
• Requires accurate data on content for each food in the diet.
• Risk of confounding with other compounds found in the same food.
– Interventions: Carry out as placebo-controlled drug trials
• Allows full control of confounding factors.
• Requires that nutrients from pills have the same effect as when
provided from the diet.
• Only relatively short term studies possible.
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Observational studies and
intervention studies
Effect of vitamin E in the diet on risk of lung cancer
Each data point represents 3380
male smokers for 6 years.
Vitamin E in the diet comes from
plant oils, nuts, vegetables,
fortified foods and many others
People with very low vitamin E
intake tend to have an unhealthy
diet in general
Data from Albanes et al. 1996
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Observational studies and
intervention studies
Effect of vitamin E in the diet on risk of lung cancer
• Supplements can benefit health
for those with a very poor diet,
who are really deficient in the
nutrient
• Supplements provide no benefit
if the diet contains enough of
the nutrient to prevent
deficiency
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Observational studies and
intervention studies
Effects of antioxidant supplementation on health
Antioxidants with no effect on
mortality:
• vitamin C
• selenium
Antioxidants that significantly
increase mortality:
• vitamin A
• beta-carotene
• vitamin E
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Examples of intervention
studies with plant foods
• Intervention studies with wholegrain foods 1. WHOLEheart
– Method: 316 overweight volunteers with low habitual wholegrain food
intake, divided into 3 groups:
– Control (no wholegrain food).
– Low (60g for 16 weeks).
– High (60g for 8 weeks, then 120g for 8 weeks).
– Range of foods provided to choose among, mostly wheat based, no
other dietary changes requested.
– 2005-2008, funder: Food Standards Agency
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Examples of intervention
studies with plant foods
• Intervention studies with wholegrain foods 1. WHOLEheart
– Result: No change in weight, cholesterol, blood pressure or other
measured outcomes.
– Increased energy intake in treatment groups.
– Brownlee et al. 2010, British Journal of Nutrition.
• Conclusion: Either the effect of whole grain consumption of
cardiovascular risk factors is too small to measure, or any
benefits are counteracted by the high sugar content of many
wholegrain foods.
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Examples of intervention
studies with plant foods
• Intervention studies with wholegrain foods 2. GrainMark
– Method: 67 volunteers, divided into 2 groups:
– Wheat, no wholegrain foods for 4 weeks, then 48g wheat whole grain
foods for 4 weeks, and then 96g for 4 weeks
– Rye, same time periods, but with rye-based whole grain foods.
– Range of foods provided to choose among within each group, standard
meal provided for the evening before measurements.
– Measurements of cholesterol content of blood, blood pressure, and
markers of intake.
– 2007-2009, funder: Food Standards Agency
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Examples of intervention
studies with plant foods
• Intervention studies with wholegrain foods 2. GrainMark
– Results: Significant improvements in both cholesterol and blood pressure
in Rye group
– Similar trends in Wheat group, but not significant.
– Increased energy intake during treatment periods.
– Haldar et al. 201?
• Conclusions: Rye has stronger effect on cardiovascular risk
factors than wheat, and a better experimental design gives
more significant results.
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Examples of intervention
studies with plant foods
Fruit at Work
• Intervention study with fruit: Fruit at Work
– Method: 409 volunteers at Durham County Hall, divided into 2 groups:
Intervention, had access to 2 pieces of fruit per day at work for 18 weeks;
Control, no change during the intervention period, but received the same
fruit for 18 weeks after the end of the measurements.
– No control of diet otherwise.
– Participants filled in questionnaires about their diet online.
– Blood pressure and weight was measured at work 3 times, 0, 9 and 18
weeks after start.
– 2008-2009, funder: European Commission
– See more on YouTube: ‘The ISAFRUIT Project: Fruit at work study’
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Examples of intervention
studies with plant foods
Fruit at Work
• Intervention study with fruit: Fruit at Work
• Results: Alinia et al., Bryant et al., Lake et al., 201?
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Examples of intervention
studies with plant foods
• Intervention study with vegetables: VegBP
• Hypothesis: That the beneficial effects of consumption of vegetables on
blood pressure is due to their content of nitrate.
• Nitrate can be taken up by the body and converted to NO.
• NO is a signal molecule that supports relaxation of blood vessels and
thereby improves blood flow and reduces blood pressure.
• Short-term intervention studies (1-6 days) with beetroot juice or pure nitrate
have shown significant reductions in blood pressure in human volunteers.
• Can this be replicated and sustained for a longer period in older people at
high risk for hypertension?
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Examples of intervention
studies with plant foods
• Intervention study with vegetables: VegBP
– Method: 225 volunteers with marginally elevated blood pressure (SBP
130-150), divided into 3 groups:
– Low nitrate: Avoid nitrate-rich vegetables in diet for 24 weeks. Receive
100g per day of nitrate-poor vegetables (20 mg nitrate) from week 8 to
week 24, to be consumed in addition to habitual diet.
– High nitrate: Avoid nitrate-rich vegetables in diet for 24 weeks. Receive
100g per day of nitrate-rich vegetables (250 mg nitrate) from week 8 to
week 24, to be consumed in addition to habitual diet.
– Intermediate: As the others, but receive 50g nitrate-rich and 50g nitratepoor vegetables (135mg nitrate) during the 16 week intervention.
– 2010-2013, funder: Food Standards Agency
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Examples of intervention
studies with plant foods
• Intervention study with vegetables: VegBP
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Examples of intervention
studies with plant foods
• Intervention study with vegetables: VegBP
• High nitrate (avoid): Lettuce, spinach, beetroot, radish, rocket, celery,
Chinese cabbage, Chinese greens, Pak choi, parsley, Swiss chard, fennel,
endive, other salad leaves, chervil, beetroot juice, rhubarb.
• Variable/inconsistent (avoid also): Watercress, celeriac, leek, green cabbage
(spring cabbage, pointed cabbage), chicory.
• Low nitrate (eat normally): Cauliflower, cucumber, gherkin, Brussels sprouts,
red cabbage, white cabbage, turnip, parsnip, pea, bean, tomato, squash,
pumpkin, onion, asparagus, potato, sweet corn, mushroom, pepper,
eggplant, garlic, sweet potato, carrot, broccoli, artichoke, Jerusalem
artichoke, any fruits, berries, fruit juices.
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Importance for public policy
and the horticultural industry
• Our knowledge about the extent and causes of the health
benefits of vegetables and fruit is extremely vague.
• Until now, all properly tested hypotheses have been disproved:
– antioxidants, fibres, minerals.
– vitamins A, C and E.
• This is the reason for the ‘5-a-day’ message: We don’t know
which vegetables or fruits are actually good for whom.
• So the only improvement that can be recommended is to
increase total volume.
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Importance for public policy
and the horticultural industry
• Our aim is to identify some more tangible benefits, with a
reproducible effect and understandable mechanism.
• If we succeed with this, then it opens a wide range of
opportunities:
– Specific health claims for particular species and/or varieties of F&V
– Quality criteria based on composition rather than appearance
– Precise recommendations for particular target groups: old, young,
overweight, diabetic, smokers etc.
– Increased awareness and credibility of the health benefits of F&V and
their roles in a healthy diet
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Importance for public policy
and the horticultural industry
• Intervention trials are important and necessary for quantification
and understanding of health benefits of foods.
• This knowledge is essential for formulation of clear, precise and
credible recommendations to the public, which can switch
attention from marketing fads to real knowledge.
• In many cases it requires radical re-thinking of most of what we
think we know about food and health.
• Commercially it will benefit some companies and harm others.
• The consumers are the certain winners.
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• Acknowledgments:
– WHOLEheart study: Iain Brownlee, Chris Seal, Sharron Kuznesof,
Wendy Bal, Susan Jebb, David Richardson.
– GrainMark study: Sumanto Haldar, Chris Seal, Wendy Bal, Manfred
Beckmann, Lee Fawcett, John Draper, Alastair Ross.
– Fruit at Work study: Charlotte Bryant, Inge Tetens, Chris Seal, Amelia
Lake, Sevil Alinia.
– VegBP study: Sumanto Haldar, Chris Seal, Wendy Bal, Roy Lamb,
Franziska Mohring, John O’Brien, Gary Ford.
Thank you for your attention!
Any questions?
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