The evidence behind our dietary guidelines

Gianluca TognonDepartment of Public Health and Community Medicine

www.gianlucatognon.it

Dietary habits in Nordic countries: common features

• High intake of milk and dairy products, moderate to high consumption of meat and a moderate consumption of vegetables and fruit

• A moderate to high intake of fish (lower in Denmark)• Potatoes and cereal products constitute as major staple

foods • Common trends in the last 2-3 decades: increased

consumption of low-fat milks and spreads, decreased total consumption of edible fats, and increased consumption of cheese, fruit and vegetables

• Cultural and culinary traditions differ among countries

Nordic Nutrition Recommendations (NNR)

• NNR give values for the intake of and balance between, individual nutrients which are adequate for development and function as well as contributing to the risk-reduction in certain diet-associated diseases

• Food-based dietary guidelines represent a ”translation” of the recommendations on energy and nutrients to foods and may include recommendations or advice on food choice, amounts, frequencies and eating pattern

NNR revision• The last NNR edition (4th) was released in 2004• A revision is ongoing, with the aim of including new

concepts from areas where new scientific knowledge has emerged

• Nutrition in specific groups (e.g. children, elderly, overweight subjects) will be also covered

• Systematic Literature Reviews (SLRs) will be performed• Established criteria for evaluating the methodological

quality of the included studies and the overall strength of the scientific evidence will be used and the work process will include several stakeholders

• The SLRs will be evaluated by external reviewers

The choice of studies to be included into SLRs

• Controlled intervention studies, prospective cohort studies, case-control studies and systematic reviews will be included

• Retrospective case-control studies where the measure of exposure occurred after or concurrent with the outcome will only be used when results from other study types won’t be available

• Cross-sectional studies will primarily be used for describing prevalence and animal studies will not be used apart from describing mechanisms

Target population• The primary target population for NNR5 is

defined as the general healthy population• This means that studies focusing on treatment

of patients with overt disease will be excluded• Studies involving subjects with increased

metabolic risks or pre-disease states, e.g. with established risk factors,

will be considered

Literature search• The search strategy will be documented, so

that the systematic reviews can be reproduced and compared with other review as well as updated as long as new findings emerge

• Preference should be for data published in peer-reviewed journals, but other sources such as official or expert reports and government funded research, may provide some valuable information

Evidence from systematic reviews and meta-analysis• Meta-analysis uses statistical methods to

combine multiple studies addressing the same research question in order to get an overall estimate

• Meta-analyses can sometimes shed new insights that individual studies failed to reveal because of power limitations

Forest plots

Advantages and disadvantages

• Potential advantages of meta-analyses include an increase in power, an improvement in precision, the ability to answer questions not posed by invidividual studies, and the opportunity to settle controversies arising from conflicting claims

• However, they also have the potential to mislead seriosly, particularly if specific study designs, within-study biases, variation across studies, and reporting biases are not carefully considered

Present Nordic Recommendations

(NNR4)

Fruit and vegetables• Important sources of several nutrients (vitamin C, folate,

potassium, fibre, carotenoids and flavonoids) associated to a low energy density

• A large body of evidence supports the hypothesis that vegetables and fruit protect from chronic disease such as cancer (lung, gastrointestinal and hormone-related), cardiovascular disease and type 2 diabetes and reduce risk factors (blood pressure, LDL-C)

• Hypothesized mechanisms include: antioxidant activity, modulation of detoxifying enzymes, stimulation of the immune system, decrease in platelet aggregation, alteration in cholesterol metabolism, modulation of steroid hormone metabolism, blood pressure reduction and even antibacterial and antiviral activity

• In addition to the contribution of these foods to nutrient intake, they may play a role in improving the dietary pattern by replacing other, less favourable foods in the diet

• An increase in vegetables and fruit consumption to at least 400 g/d would reduce the cancer incidence by 20% in Sweden

• An increase in the vegetable and fruit consumption level to 600 g/d has been estimated to be associated with a 10-20% reduction in cardiovascular disease incidence

Potatoes• Common staple food in Nordic countries

contributing starch as well as several nutrients (potassium, vitamin B6, vitamin C and fibre)

• Boiled generally have a high glycaemic index, but also a high satiating effect

• Based on the glycaemic properties of potatoes and the lack of data of a protective effect of potatoe consumption on chronic disease risk, a restricted consumption of potatoes has been recommended by some researchers

• In some epidemiological studies, dietary patterns including a high consumption of potatoes have been associated with increased risk of T2D, CHD and weight gain

• However, in many of these studies potatoes were reported as fried and were generally associated with a dietary pattern characterized by a high consumption of meat and high-fat and high-sugar foods and a low consumption of fruit, vegetables and fibre-rich cereals

• In other studies based on dietary patterns, consumption of e.g. baked potatoes and sweet potatoes was more frequent in healthy eating patterns (high consumption of fruit and vegetables, low-fat dairy products and whole grains) and was associated with a lower mortality (e.g. Mediterranean diet)

Cereals• A major source of carbohydrate and dietary fibre

in the Nordic diet• Wholegrain products in particular, provide nutrients such as K, Mg,

vitamin E, folate and antioxidants• Several observational studies support the beneficial role of

wholegrain consumption or cereal fibre in reducing the risk of CVD and total mortality

• High wholegrain consumption has also been inversely associated with chronic disease risk

• The phytochemicals of wholegrain cereals may serve as both antioxidants and phytoestrogens

• The potential beneficial effects of wholegrain food include lowering of serum total and LDL-cholesterol, in some cases also hypotriglyceridaemic effects, antioxidant properties and possibly also antithrombotic and decreased platelet-aggregating effects

Fish and seafood• Regular fish intake, both fatty and lean, contributes to

iodine, selenium, vitamin D and n-3 fatty acids intake, and is recommended as part of a balanced diet

• Fatty fish, is a major source of long-chain n-3 fatty acids• A moderate amounts of fish or n-3 fatty acids from fish is

associated with a lower risk of fatal CHD and in particular sudden cardiac death, probably via anti-arrhythmic effects

• The protective effect of fish intake against CHD and related diseases could also be attributable to constituents other than n-3 fatty acids such as proteins

Milk and dairy products

• Milk, fermented milks and cheese are traditional foods in the Nordic diet

• Milk provides several nutrients e.g. calcium, potassium, riboflavin and selenium

• Cheese contains largely similar amounts of nutrients on an energy basis, except for e.g. lactose and potassium, which are concentrated in the whey

• Dairy fats are rich in saturated fatty acids, a good reason for recommending low-fat products

• Milk or fermented milk product intake has in some earlier studies been shown to have less pronounced effects on serum lipids than expected from their fat content

• Many of the studies included very large amounts of milk, which could have affected the general dietary composition

• More recent intervention studies in humans including mainly fermented milk products containing different bacteria strains have shown varying results

• Due to their high content of calcium, dairies have been promoted for adequate bone formation during childhood and the prevention of post-menopausal osteoporosis

• Adequate or high intakes of calcium seem to increase bone density in adolescence and supplementation with calcium or milk has similar effects in older women

Meat and meat products• Traditional foods in the Nordic diet contributing

protein, readily available iron, selenium, zinc and a range of B vitamins

• Due to the relatively high proportion of SAFA, high consumption of fatty meat and meat products can contribute to increased LDL-C levels

• Processed meat products usually contain relatively high amounts of sodium (salt)

• Inclusion of lean meat into the diet improves iron availability and status without providing too many fats

• High consumption of meat, especially red (beef, pork, sausages) and processed meat (cold cuts) has been regarded as risk factor for colorectal cancer

• Meat may contain harmful components formed during cooking (heterocyclic amines and polycyclic aromatic hydrocarbons), processing (nitrates and nitrites) or during intestinal metabolism (N-nitroso compounds)

• The carcinogenic potential of these compounds may be dimished by avoiding exposure of meat surfaces to flames and high temperatures and also by increasing dietary intake of protective constituents derived from plant foods

• Meat and meat products provide a wide range of nutrients and consumption of moderate amounts of meat, preferably lean, is recommended as part of a balanced and varied diet

Edible fats• Edible fats, e.g. butter, margarines and vegetable oils,

are the major sources of fat in the Nordic diet• The recommendations on choice of fats emphasise a

limitation of saturated and trans fatty acids, and an increase in n-3 fatty acids but not of n-6 fatty acids

• Soft or fluid vegetable fats, low in saturated and trans fats, should primarily be chosen

• A good n-3/n-6 proportion can be achieved using rapeseed oil and rapeseed oil based fats, in addition to other good sources such as fish and seafood

Energy-dense and sugar-rich foods

• Foods rich in fat and/or refined sugars, such as soft drinks, sweets, snacks and sweet bakery products, mainly contribute ”empty calories”

• A frequent consumption decreases the nutrient density and increases the risk of nutritional imbalance and inadequacy and also dental caries

• A high intake of refined sugars in fluid form, e.g. soft drinks, may increase the risk of overweight

Salt intake• The recommendation on sodium (salt) is

mainly based on effects on blood pressure• A major factor in order to achieve the

recommended salt intake is a reduction in the sodium levels in many processed foods

• In addition, household and individual use of table salt need to be moderated

Key recommendationsFoods and components to reduce• < 2,300 mg/day of sodium and < 1,500 mg/day among

persons who are 51 and older and those of any age who have hypertension, diabetes, or chronic kidney disease

• < 10% of calories from saturated fatty acids by replacing them with unsaturated fatty acids

• < 300 mg/day of dietary cholesterol• trans fatty acid consumption as low as possible by limiting

hydrogenated oils and other solid fats • Reduce the intake of calories from solid fats and added sugars• Limit the consumption of foods that contain refined grains,

especially if they also contain solid fats, added sugars, and sodium• If alcohol is consumed, it should be consumed in moderation: up to

one drink per day for women and two drinks per day for men

Foods and nutrients to increase • Increase vegetable and fruit intake• Eat a variety of vegetables, especially dark-green and red and

orange vegetables and beans and peas• Consume at least half of all grains as whole grains• Increase intake of fat-free or low-fat milk and milk products• Choose a variety of protein foods, including seafood, lean

meat and poultry, eggs, beans and peas, soy products, and unsalted nuts and seeds

• Replace some meat and poultry with seafood• Use oils instead of solid fats where possible• Choose foods that provide more potassium, dietary fiber,

calcium, and vitamin D, such as vegetables, fruits, whole grains, and milk and milk products

Healthy eating patterns

• The DASH eating pattern and its variations have been tested in several clinical trials

• DASH emphasizes vegetables, fruits, and low-fat milk and milk products; includes whole grains, poultry, seafood, nuts and is lower in sodium, red and processed meats, sweets, and sugar-containing beverages

• Modifications containing higher levels of either unsaturated fatty acids or protein have been tested

• In research studies, each of these DASH-style patterns lowered blood pressure, improved blood lipids, and reduced cardiovascular disease risk as well as mortality compared to diets that were designed to resemble a typical American diet

• The DASH-Sodium study on hypertension also reduced sodium, and resulted in lower blood pressure in comparison to the same eating pattern, but with a higher sodium intake

The DASH Diet

• The first evidence of the beneficial effects of the Mediterranean diet came years ago from the Seven Country Study (Keys, 1980)

• The general features of this pattern are a high or moderately high intake of: – cereals (that in the past were largely unrefined)– olive oil (and therefore MUFA)– fruit, vegetables and legumes – nuts and seeds – fish (according to the proximity of the sea, and therefore PUFA)– alcoholic beverages, but mostly red wine, generally during meals

(Willett et al., 1995)• And a low or moderately low intake of

– dairy products (mostly in the form of cheese and yogurt)– meat and meat products (and therefore SAFA)

The Mediterranean diet

• The Mediterranean diet was first considered protective against CHD (de Lorgeril et al., 1999)

• Recently a longitudinal study showed that MD was associated with a higher preservation of ventricular function and a more favourable prognosis after an acute coronary event (Chrysohoou, et al., 2010)

• In other studies, beneficial effects on total mortality have been discovered (Trichopoulou et al., 2005)

• A Mediterranean dietary pattern has also been shown to increase longevity among European elderly of the HALE project (Knoops et al., 2004)

• In addition, a recent paper on the Swedish population showed a reduction in total mortality among young women (Lagiou et al., 2006)

Mediterranean diet and mortality

Food groups (g/day) Overall mean(N = 1,037)

Median intakes and 95% CLs (g/day)

p for trend across birth cohorts

Vegetables and potatoes 237.6 ± 98.7 ♀: 209.5 (99.6; 406.3)♂: 239.0 (120.1; 432.2) < 0.0001

Fruit 196.6 ± 146.3 ♀: 176.4 (22.3; 527.7)♂: 155.5 (14.0; 456.0)

< 0.0001

Legumes nuts and seeds 15.2 ± 20.2 ♀: 2.0 (0; 40.0)♂: 13.3 (0; 60.0)

< 0.0001

Total cereals 207.4 ± 104.0 ♀: 165.0 (68.2; 383.0)♂: 213.0 (98.3; 442.1)

(-) < 0.0001

- Wholegrain cereals 107.9 ± 95.6 ♀: 74.2 (0; 298.5)♂: 92.8 (0; 322.0) (-) < 0.0001

Fish and fish products 53.8 ± 35.8 ♀: 45.2 (12.8; 105.3)♂: 53.7 (13.8; 129.5) < 0.0001

Dairy products 445.1 ± 251.7 ♀: 373.3 (127.9; 829.5)♂: 446.0 (74.0; 1061.9) 0.41

Meat, meat products, eggs 129.5 ± 55.3 ♀: 110.1 (47.9; 187.3)♂: 137.7 (66.3; 251.1) < 0.001

- Meat and meat products 105.4 ± 47.9 ♀: 89.7 (38.4; 168.8)♂: 109.1 (52.5; 204.9) < 0.0001

Red wine 2.0 ± 4.7 ♀: 0 (0; 9.8)♂: 0 (0; 10.7) < 0.001

Mean and median intakes of different food groups in the H70 elderly study in Gothenburg

Mediterranean diet score across birth cohorts

1901 (N = 323)

1911 (N = 214)

1922 (N = 88)

1930 (N = 412)

Overall(N =

1,037)

p for trend

Refined mMDS (mean ± SD)

4.3 ± 1.6 4.0 ± 1.6 4.8 ± 1.5 4.8 ± 1.8 4.5 ± 1.7

< 0.001Medians (5th;95th perc)

4 (2; 7) 4 (1; 7) 5 (2; 7) 5 (2; 8) 4 (2; 7)

HALE mMDS(mean ± SD)

4.1 ± 1.5 3.6 ± 1.4 4.1 ± 1.4 4.1 ± 1.6 4.0 ± 1.5

0.02Medians (5th;95th perc)

4 (2; 6) 4 (1; 6) 4 (2; 6) 4 (1; 7) 4 (2; 6)

Mediterranean diet and mortality

Mediterranean diet score (MDS) HR 95% CLs

MDS 0.93 (0.89; 0.98)

- Crude estimate 0.92 (0.88; 0.97)

- Highest 4 levels vs the others 0.82 (0.67; 0.99)

- Crude estimate 0.81 (0.67; 0.99)

High intake/level of: HR 95% CLs

- Vegetables and potatoes 1.06 (0.90; 1.24)

- Fruit 1.03 (0.87; 1.21)

- Legumes, nuts and seeds 0.98 (0.83; 1.16)

- Cereals 1.01 (0.86; 1.19)

- Wholegrain cereals 0.85 (0.73; 1.00)

- Fish 0.96 (0.82; 1.13)

- Alcohol 0.77 (0.61; 0.97)

- MUFA/SAFA ratio 0.98 (0.84; 1.15)

- (MUFA + PUFA)/SAFA ratio 0.96 (0.82; 1.13)

Low intake of:

- Dairy products 0.82 (0.70; 0.96)

- Meat and meat products 0.89 (0.76; 1.05)

- Meat, meat products and eggs 0.84 (0.71; 0.98)

Food groups

Final considerations• Studies of dietary patterns are inherently

complex• However, there is a convergence of evidence on

the fact that dietary patterns associated with longevity emphasize fruits and vegetables and are reduced in saturated fat, meats, refined grains, sweets, and full-fat dairy products

• We hope is that the results of the present research will stimulate a productive discussion on these issues and be considered in updated food- and nutrient-level guidelines for the Swedish population

THANKS FOR YOUR ATTENTION!