Nutrition library
Nutrition Library
Nutrition research explained in plain English, free for everyone, plus members-only fact sheets you can download as PDFs.
Research & studies
Nutrition research
Each write-up explains what a study found, how it was done and where its limits are — so you can see how strong the evidence really is.
Can eating more fermented foods change your gut microbiome?
In a small Stanford study, adults who gradually increased fermented foods — yoghurt, kefir, kimchi, kombucha and fermented vegetables — to around six servings a day saw the variety of their gut bacteria increase, and several blood markers of inflammation fall.
- Design
- Randomised trial
- People
- 36 healthy adults
- Length
- 17 weeks
Vitamin K2 and the heart: what the Rotterdam Study found
In a large Dutch population study, people who ate the most vitamin K2 (menaquinone) had a lower risk of dying from coronary heart disease than those who ate the least.
- Design
- Prospective cohort
- People
- 4,807 adults, 55+
- Follow-up
- ~7–10 years
How much fibre do we really need? A major review of the evidence
Pooling decades of research, this review found that people eating the most fibre had a 15–30% lower risk of dying early, and of heart disease, stroke, type 2 diabetes and bowel cancer, than people eating the least.
- Design
- Systematic reviews & meta-analyses
- Evidence
- 185 cohort studies, 58 trials
- Commissioned by
- WHO
Omega-3 supplements and heart health: the VITAL trial
In this very large trial, taking 1 g of fish-oil omega-3 daily did not significantly reduce the main combined measure of heart attacks, strokes and cardiovascular deaths in generally healthy adults.
- Design
- Randomised placebo-controlled trial
- People
- 25,871 US adults
- Length
- Median 5.3 years
Do vitamin D supplements prevent cancer or heart disease?
Taking 2,000 IU of vitamin D a day for around five years didn’t lower rates of cancer or major cardiovascular events in generally healthy adults.
- Design
- Randomised placebo-controlled trial
- People
- 25,871 US adults
- Dose
- 2,000 IU (50 µg) / day
Vitamin K2 and bone loss after menopause: a 3-year trial
In this Dutch trial, healthy postmenopausal women who took a daily vitamin K2 (MK-7) supplement for three years lost less bone density at the spine and hip than women taking a placebo.
- Design
- Randomised placebo-controlled trial
- People
- 244 postmenopausal women
- Dose
- 180 µg MK-7 a day
Can vitamin K2 reduce arterial stiffness?
Using the same group of women as the bone study, researchers found that three years of vitamin K2 (MK-7) improved measures of arterial stiffness, particularly in women whose arteries were stiffest at the start.
- Design
- Randomised placebo-controlled trial
- People
- 244 postmenopausal women
- Length
- 3 years
What actually counts as a fermented food? The expert consensus
An international expert panel agreed a clear definition: fermented foods are made through the deliberate growth of microbes.
- Design
- Expert consensus statement
- Panel
- International Scientific Association for Probiotics and Prebiotics
- Focus
- Definition and health evidence
Why 30 plants a week? The American Gut Project
This is where the popular ‘30 plants a week’ idea comes from.
- Design
- Citizen-science observational study
- People
- Over 11,000 participants
- Countries
- Mainly US, UK and Australia
Whole grains and long-term health: a major BMJ review
Pooling dozens of long-term studies, researchers found that people eating about three servings (90 g) of whole grains a day had a lower risk of heart disease, cancer and dying early than people eating few or none..
- Design
- Systematic review and dose-response meta-analysis
- Evidence
- 45 prospective studies
- Comparison
- Per 90 g of whole grains a day
Does fibre protect your heart? Evidence from 22 studies
Each extra 7 g of fibre a day, roughly a portion of beans plus a portion of fruit or vegetables, was linked to about a 9% lower risk of cardiovascular disease and coronary heart disease..
- Design
- Systematic review and meta-analysis
- Evidence
- 22 cohort studies
- Comparison
- Per 7 g of fibre a day
REDUCE-IT: high-dose EPA in people with high triglycerides
In people with heart disease or diabetes, raised triglycerides and already taking statins, a prescription-strength dose of purified EPA (a type of omega-3) reduced heart attacks, strokes and other cardiovascular events by about a quarter compared with placebo..
- Design
- Randomised placebo-controlled trial
- People
- 8,179 adults at high cardiovascular risk
- Dose
- 4 g a day purified EPA (icosapent ethyl)
ASCEND: omega-3 supplements in people with diabetes
In a large UK trial of adults with diabetes but no heart disease, a standard 1 g daily omega-3 supplement did not reduce heart attacks or strokes compared with an olive oil placebo..
- Design
- Randomised placebo-controlled trial
- People
- 15,480 UK adults with diabetes
- Length
- Average 7.4 years
Vitamin D and colds: a major analysis of 25 trials
Across 25 trials, vitamin D supplements slightly reduced the risk of acute respiratory infections such as colds and flu.
- Design
- Individual participant data meta-analysis
- Evidence
- 25 randomised trials
- People
- About 11,000 participants
Do vitamin D supplements protect bones? A large meta-analysis
In adults who were not deficient, vitamin D supplements on their own did not prevent fractures or falls, or meaningfully improve bone density.
- Design
- Systematic review and meta-analysis
- Evidence
- 81 randomised trials
- People
- Over 53,000 participants
Members only
Fact sheets
Clear, referenced guides to nutrients, foods and conditions: what they are, why they matter and what to eat. Each one can be downloaded as a PDF.
Members only
Join to unlock the fact sheets
The Nutrition Library is for DOIG Nutrition members. Membership includes:
- All fact sheets and guides, with printable PDFs
- Condition guides, including IBS & low FODMAP, coeliac disease and bone health
- Practical tools such as the Salad Builder and the balanced-plate guide
- New fact sheets as they’re published
Preview: this demo lets anyone in. On the live site, accounts are created and checked securely by the website platform.
23 fact sheets
The Balanced Plate
MembersThe UK Eatwell Guide, explained
Salad Builder
MembersSay goodbye to boring salads: five mix-and-match steps to a filling, energising bowl
Hormone-Supportive Salads
MembersTen fibre-rich salad recipes, each serving four
Inflammation & Anti-Inflammatory Eating
MembersWhat chronic inflammation is, and the eating pattern associated with lower levels
IBS & the Low FODMAP Diet
MembersUnderstanding irritable bowel syndrome, and how to use the low FODMAP diet to find your triggers
Nutrition for Coeliac Disease
MembersLiving well gluten-free: what to avoid, what to focus on and how to prevent cross-contamination
Fermented Foods
MembersFood transformed by microbes, and how to include it in your diet
Fibre
MembersFoods rich in fibre: what to eat and why
Bone Health & Osteoporosis
MembersNutrition and lifestyle for stronger bones, including through the menopause
Goitrogens & Your Thyroid
MembersDo you need to avoid them? For most people, no.
Stress & the HPA Axis
MembersHow your stress system works, and the everyday habits that support it
Sensitive Skin Routine
MembersSimple, effective steps to clearer skin and a healthy skin barrier
Balancing Blood Sugar
MembersHow to avoid the energy highs and lows, and eat for steadier energy
Low Glycaemic Load Foods
MembersChoosing carbohydrates that release energy slowly
Starchy Vegetables & Root Carbs
MembersCarbohydrate sources beyond bread and pasta
The Paleo Diet
MembersWhat it is, what the evidence says, and how to do it well
Intermittent Fasting
MembersTime-restricted eating: what it is and what the evidence shows
Stopping Smoking
MembersWhy it matters for your heart, and practical ways to quit
Omega-3
MembersEssential fats from oily fish, seeds and nuts
Vitamin K2
MembersThe fermented-food vitamin
Vitamin D
MembersThe sunshine vitamin in a northern country
Magnesium
MembersA quiet mineral with a long job list
Natto
MembersJapan’s fermented soybean
In preparation