Dietary Strategies for Metabolic Syndrome: A Comprehensive Review

Authors, Journal, Affiliations, Type, DOI

• Sara Castro-Barquero, Ana María Ruiz-León, Maria Sierra-Pérez, Ramon Estruch, Rosa Casas
• Nutrients 2020, 12(10), 2983
• University of Barcelona; IDIBAPS; CIBEROBN / Instituto de Salud Carlos III, Madrid (PREDIMED-Plus affiliated group)
• Type: Comprehensive narrative review
• DOI: https://doi.org/10.3390/nu12102983

Overview

This 2020 Spanish review benchmarks seven dietary patterns — Mediterranean, DASH, plant-based, low-carbohydrate/ketogenic, low-fat, high-protein, and Nordic — against all five components of metabolic syndrome (MetS): central obesity, dyslipidemia, elevated blood pressure, impaired glucose metabolism, and low HDL-c. The review concludes that the Mediterranean diet is the strongest comprehensive strategy for MetS prevention and treatment, with DASH having the most evidence specifically for blood pressure reduction. Ketogenic and low-fat diets show short-term benefits but have limitations for long-term MetS management. Dietary adherence is identified as the single most important determinant of outcomes regardless of dietary pattern.

Keywords

Metabolic syndrome; dietary pattern; Mediterranean diet; plant-based diet; DASH diet; low-carbohydrate diet; high-protein diet; low-fat diet

Key Takeaways

1. Introduction and MetS Epidemiology

• MetS is defined by ≥3 of: central obesity, dyslipidemia, impaired glucose metabolism, elevated BP, and low HDL-c (IDF/AHA/NHLBI harmonised consensus definition)
• Prevalence in developed countries: 20–25% of adults; Spain: ~22.7%; incidence increases with age
• MetS increases T2DM risk 2-fold and major CVD events 5-fold; also raises risk of cancer, NAFLD, neurodegenerative disease, and all-cause mortality
• Lifestyle modifications, especially dietary habits, are the primary therapeutic strategy for MetS management

2. Mediterranean Diet

• Characterised by high intake of vegetables, fruits, whole grains, pulses, nuts, and EVOO (35–45% kcal from fat, mainly MUFA/PUFA; 15% protein; 40–45% CH); moderate red wine with meals; low red meat, butter, and sweets
• EVOO is the primary source of MUFAs; oleic acid linked to improvements in insulin resistance, blood lipids, and BP
• Polyphenols from EVOO, fruits, and vegetables provide anti-inflammatory and antioxidant effects
• Meta-analysis of 12 cross-sectional/prospective cohorts: higher MedDiet adherence → 19% lower MetS risk (RR 0.81; 95% CI 0.71–0.92); waist circumference (RR 0.82) and BP (RR 0.87) also improved
• CARDIA study (n=4,713, US): HR 0.67 (95% CI 0.49–0.90) for MetS with high adherence
• SU.VI.MAX study (n=3,232, France, 6-year follow-up): 53% lower MetS risk (OR 0.47–0.50) in highest MedDiet tertile
• Korean adults: medium-to-high MedDiet adherence OR 0.73–0.64 for MetS
• US Women's Health Study (n=25,994): CVD HR 0.72 (95% CI 0.61–0.86) with highest MedDiet score
• MedDiet reduces T2DM and CVD incidence and severity; considered first-line strategy for MetS

3. DASH Diet

• Characterised by low total fat (27% kcal), saturated fat (6%), dietary cholesterol (~150 mg/d), and sodium (1500–2300 mg/d); high fiber (>30 g/d), potassium, magnesium, and calcium
• Meta-analysis 30 RCTs (n=5,545): DASH with lifestyle intervention → SBP −3.2 mmHg (95% CI −4.2 to −2.3), DBP −2.5 mmHg (95% CI −3.5 to −1.5) vs control diet
• BP reduction more pronounced when sodium <2400 mg/d, age <50, and hypertension without medication
• Network meta-analysis vs 13 dietary patterns: DASH most effective for BP management, especially vs low-fat diets
• Cross-sectional study (n=1,493 adults): high DASH adherence → 48% less risk of MetS; lower BMI, waist circumference, inflammatory markers, and adiposity
• Paediatric data (n=425, age 6–18): high DASH adherence → 64% lower MetS risk; inverse associations with BP, fasting glucose, and abdominal obesity
• Meta-analysis (multiple cohort studies): higher DASH adherence → RR 0.78 all-cause mortality, RR 0.78 CVD mortality, RR 0.84 cancer mortality, RR 0.82 T2DM
• Reduction in BMI (WMD −0.42 kg/m²) and waist circumference (−1.05 cm) demonstrated in middle-term interventions

4. Plant-Based Diets

• Spectrum includes vegan, lacto-vegetarian, lacto-ovo-vegetarian, and pescatarian patterns; increasingly applied to include MedDiet as a predominantly plant-based approach
• Vegetarian diet meta-analysis (7 RCTs): SBP −4.8 mmHg (95% CI −3.1 to −6.6), DBP −2.2 mmHg (95% CI −1.0 to −3.5)
• Observational meta-analysis (32 studies): vegetarian diet → SBP −6.9 mmHg, DBP −4.7 mmHg
• Meta-analysis of 11 RCTs: vegetarian diet → reduced total cholesterol, LDL-c, and HDL-c vs omnivorous; no significant effect on triglycerides; weight loss −2.88 kg
• MedDiet, DASH, and vegetarian diet → 38%, 20%, and 28% lower coronary heart disease risk, respectively
• Key mechanism: MUFA/PUFA profile replacing SFA → anti-inflammatory and improved insulin sensitivity; polyphenols and antioxidants contribute
• Caution: "plant-based" does not equal "healthy" — refined grains, pastries, and SSBs are plant-derived but harmful

5. Low-Carbohydrate Diet

• Low-CH defined as <50% kcal from CH; very low (ketogenic) as <10% CH (~30–50 g/d)
• Meta-analysis (18 studies, n=69,554): 2.5% increase in MetS risk per 5% energy from CH (95% CI 0.4–4.8)
• RCT (Bazzano et al.): low-CH (<40% kcal) vs low-fat (no energy restriction): greater weight loss −3.5 kg, fat mass −1.5%, improved TG, HDL-c, and TC:HDL ratio at 1 year
• In T2DM, low-CH vs low-fat: higher reductions in weight, HbA1c, TG, and BP; increased HDL-c; modification of glucose-lowering medications
• PURE cohort (n=135,335, 18 countries): dietary pattern 50–55% CH showed lowest mortality; U-shaped association (high >70% or low <40% CH both increased total mortality)
• Seidelmann et al.: low-CH diets rich in animal-derived fat/protein → increased mortality; plant-based fat/protein sources recommended
• Ketogenic meta-analysis (Bueno et al.): greater weight loss (WMD −0.91 kg), reduced TG (−0.18 mmol/L), reduced DBP (−1.43 mmHg), increased HDL-c (+0.09 mmol/L) vs low-fat diet
• Ketogenic mechanism: reduced insulin secretion → inhibited lipogenesis → increased lipolysis; satiety via protein + leptin/ghrelin modulation; ketone body production
• Weight/CVD benefits of ketogenic diet likely due to energy restriction, not macronutrient distribution per se

6. Low-Fat Diet

• Defined as <30% kcal total fat (<10% SFA); higher CH (50–60% kcal) and moderate protein (15–17%)
• Meta-analysis (34 RCTs): 18% lower all-cause mortality in obese adults with weight-loss low-fat interventions (95% CI 0.71–0.95)
• Short-term BP and lipid improvements (SBP, DBP, HDL-c, LDL-c) vs usual diet; attenuated in long-term vs MedDiet and DASH
• Clinical trials on low-fat and MetS: conflicting results; no significant effects on CVD/CHD in postmenopausal women; no lower MetS prevalence in older high-CVD-risk subjects
• DIETFITS trial (Gardner et al.): low-fat and low-CH produced equal significant weight loss — no difference between groups
• Veum et al.: low-fat vs very high-fat diets showed no significant differences in MetS criteria, body weight, or body composition
• Current dietary guidelines should not set upper limits on total fat intake from healthy unsaturated sources; SFA should remain <10% energy; replace SFA with MUFA/PUFA

7. High-Protein Diet

• Defined as 20–30% kcal from protein (~1.34–1.5 g/kg body weight/day)
• Meta-analysis (18 studies, T2DM): high-protein diet did NOT significantly decrease body weight, glycemic control, lipids, or BP vs regular protein; triglyceride reduction was the one consistent benefit
• RCT (Campos-Nonato, n=118 MetS adults): hypocaloric high-protein diet → greater weight loss (−7.0 kg vs −5.1 kg, p=0.046); MetS criteria improved in both arms but no between-group difference
• OmniHeart study (n=164): unsaturated fat diet (not high-protein diet) improved insulin sensitivity; protein diet did not affect insulin sensitivity
• Mechanism: protein-induced satiety reduces subsequent energy intake; protein preserves muscle mass during energy restriction
• Red meat and processed meat associated with higher T2DM, CVD, and MetS risk; plant-based protein sources (soy, legumes, nuts) preferred
• Meta-analysis (36 RCTs): substitution of red meat with plant-based protein → reduced total cholesterol and LDL-c

8. Other Dietary Patterns and Strategies

• Nordic diet: high whole-grain fiber products (rye, barley, oat), rapeseed oil as main fat, high fish; meta-analysis 5 RCTs (n=513): SBP −3.97 mmHg, DBP −2.08 mmHg, LDL-c improvement; further studies needed
• Intermittent fasting: caloric restriction strategy → weight loss, improved insulin resistance, dyslipidaemia, BP reduction, decreased T2DM/CVD risk; complex applicability requiring supervised health professional guidance
• Other approaches: omega-3 FA, low glycaemic index, high antioxidant capacity, high-meal-frequency interventions

9. Conclusions

• Protective effects of healthy dietary patterns on MetS derive from cumulative small dietary changes rather than restriction of any single nutrient
• MedDiet is the paradigm for MetS prevention and treatment when compared to low-fat and very restricted diets
• Dietary quality > dietary quantity for MetS management and prevention
• Adherence is the decisive factor regardless of dietary pattern type
• Energy-restricted dietary patterns and increased physical activity remain crucial for MetS patients

Limitations of the Document

• Narrative/comprehensive review design, not systematic meta-analysis; susceptibility to selection bias in study inclusion
• Heterogeneity in MetS definitions across included studies complicates comparisons
• Intervention duration varies widely across included RCTs — short-term benefits of low-fat/low-CH diets may not persist long-term
• Most data from European/Spanish populations (especially PREDIMED-Plus studies); generalisability to other populations uncertain
• Ketogenic and very-low-CH diet long-term cardiovascular safety data insufficient for strong recommendations
• Industry funding not consistently reported across primary studies included

Key Concepts Mentioned

• concepts/Metabolic-Syndrome — central subject; definition, epidemiology, dietary strategies
• concepts/Heart-Healthy-Dietary-Patterns — DASH, Mediterranean, plant-based, low-fat, high-protein, Nordic patterns vs MetS
• concepts/Blood-Pressure-Target-T2DM — DASH and MedDiet BP effects; T2DM management context

Key Entities Mentioned

• entities/Hypertension — BP reduction is a primary MetS criterion; DASH most effective pattern for BP
• entities/Heart-Failure — incidentally referenced in context of CAM and nutrition

Wiki Pages Updated

• wiki/sources/diet-mets-nutrients-2020.md — created (this file)
• wiki/concepts/Metabolic-Syndrome.md — created
• wiki/concepts/Heart-Healthy-Dietary-Patterns.md — updated with MetS-specific dietary pattern data
• wiki/sourceindex.md — updated
• wiki/wikiindex.md — updated