Effect of high-carbohydrate or high-monounsaturated fatty acid diets on blood pressure: a systematic review and meta-analysis of randomized controlled trials

Relationships between sodium, fats and carbohydrates on blood pressure, cholesterol and HbA1c: an umbrella review of systematic reviews

Background

The relationship between nutrition and health is complex and the evidence to describe it broad and diffuse. This review brings together evidence for the effect of nutrients on cardiometabolic risk factors.

Methods

An umbrella review identified systematic reviews of randomised controlled trials and meta-analyses estimating the effects of fats, carbohydrates and sodium on blood pressure, cholesterol and haemoglobin A1c (HbA1c). Medline, Embase, Cochrane Library and Science Citation Index were search through 26 May 2020, with supplementary searches of grey literature and websites. English language systematic reviews and meta-analyses were included that assessed the effect of sodium, carbohydrates or fat on blood pressure, cholesterol and HbA1c. Reviews were purposively selected using a sampling framework matrix. The quality of evidence was assessed with A MeaSurement Tool to Assess systematic Reviews 2 (AMSTAR2) checklist, evidence synthesised in a narrative review and causal pathways diagram.

Results

Forty-three systematic reviews were included. Blood pressure was significantly associated with sodium, fibre and fat. Sodium, fats and carbohydrates were significantly associated with cholesterol. Monounsaturated fat, fibre and sugars were associated with HbA1c.

Conclusion

Multiple relationships between nutrients and cardiometabolic risk factors were identified and summarised in an accessible way for public health researchers. The review identifies associations, inconsistencies and gaps in evidence linking nutrition to cardiometabolic health.

Association between Macronutrient and Fatty Acid Consumption and Metabolic Syndrome: A South African Taxi Driver Survey

We aimed to examine the association between macronutrient and fatty acid intake and metabolic syndrome (MetS) and its components in South African male mini-bus taxi drivers. One hundred and eighty-five (n = 185) male taxi drivers, aged 20 years and older, who operate in the Cape Town metropole, South Africa, were included. The International Diabetes Federation (IDF) algorithm was used to define MetS. The association between macronutrient and fatty acid intake (assessed using 24 h recall) and MetS were analyzed using multivariable nutrient density substitution models. Overall, protein consumption significantly increased the likelihood of high blood pressure (HBP) and significantly lowered the likelihood of having low levels of high-density lipoprotein cholesterol (HDL-C). In an isoenergetic state, the intake of protein instead of carbohydrates (CHOs) and total fat, reduced the likelihood of elevated triglycerides by 6.7% and 6.6%, respectively. The intake of CHOs instead of protein and total fat, reduced the likelihood of HBP by 2.2% and 2.8%, respectively. In the same isoenergetic state, the intake of saturated fatty acids (SFAs) instead of mono-unsaturated fatty acids (MUFAs) increased the likelihood of HBP by 9.8%, whereas the intake of polyunsaturated fatty acids (PUFAs) instead of SFAs decreased the likelihood of HBP by 9.4%. The current study showed that when total food energy intake is kept constant, a diet that is high in protein, CHOs and PUFAs reduces triglycerides and BP, whereas the intake of total fat and SFAs had the opposite effect. It should, however, be noted that these outcomes were produced using mathematical models, as such we recommend further prospective studies in real life that will reveal the actual associations between the consumption of macronutrients and fatty acids and MetS and its components.

The Effect of a Peanut-Enriched Weight Loss Diet Compared to a Low-Fat Weight Loss Diet on Body Weight, Blood Pressure, and Glycemic Control: A Randomized Controlled Trial

The objective of this study was to examine the effect of consuming 35 g of peanuts prior to two main meals per day as part of a weight loss diet, compared to a traditional low-fat weight loss diet, on body weight, markers of glycemic control, and blood pressure in adults at risk of type 2 diabetes over 6 months. A two-arm randomized controlled trial was conducted. Adults (age > 18 years) with a BMI of >26 kg/m2 at risk of type 2 diabetes were randomized to the peanut group or the traditional low-fat-diet group (control). The peanut group was advised to consume 35 g of lightly salted dry-roasted peanuts prior to two main meals per day. Participants in the control group were given education to follow a low-fat diet. Both groups had dietetic counseling to restrict energy intake (women: <5500 kJ/1300 kcal/d; men: <7000 kJ/1700 kcal/d). Outcome assessment occurred at baseline, 3 months, and 6 months. In total, 107 participants were randomized (65% female; mean age 58 ± 14 years, BMI 33 ± 5.4 kg/m2, waist circumference 109 ± 13 cm, AUSDRISK score 15 ± 5 points), and 76 participants completed the study. No between-group difference in body weight (primary outcome) was observed at 6 months (mean difference, −0.12 kg; 95% CI, −2.42, 2.18; p = 0.92). The mean weight loss at 6 months was 6.7 ± 5.1 kg in the cohort (visit p < 0.001). HbA1c, fasting glucose, fasting insulin, 2-h glucose, and HOMA-IR were not different between the groups. Systolic blood pressure was reduced to a greater extent in the peanut group vs. the control group at 6 months (−5.33 mmHg; 95% CI, −9.23, −1.43; p = 0.008). Intake of 35 g of peanuts prior to two main meals per day, in the context of an energy-restricted diet, resulted in weight loss comparable to a traditional low-fat weight loss diet without preloads. Greater systolic blood pressure reductions were observed with peanut intake, which may lower cardiovascular disease risk.

Use of GRADE in evidence syntheses published in high-impact-factor nutrition journals: A methodological survey

OBJECTIVE

To identify and describe the use of the GRADE approach for rating the certainty of evidence in nutrition systematic reviews (SRs).

STUDY DESIGN AND SETTING

We systematically searched for SRs using GRADE that were published between 2015 and 2019 in the 10 "nutrition" journals with the highest impact factor according to the JCR 2018.

RESULTS

Out of 800 SRs, 55 SRs of randomized control trials (RCTs) and/or nonrandomized studies (NRSs) used GRADE. Forty-seven SRs (5.9%) rated the outcome specific certainty of evidence (n = 36 in 2018/2019). We identified a total of 465 certainty of evidence outcome ratings (n = 335 RCT ratings), ranging from very-low (28.8%) to low (41%), moderate (26.5%), and high (3.7%). Very-low and high certainty of evidence ratings accounted for 61.4% and 0.8% of ratings in SRs of NRSs, compared to 16.1% and 4.8% in SRs of RCTs. Certainty of evidence was downgraded mostly for risk of bias (37.8%) and imprecision (33%) in SRs of RCTs and for imprecision (32.7%), risk of bias (29.4%) and inconsistency (29%) in SRs of NRSs.

CONCLUSION

Our study suggests a need for directing more attention toward strengthening acceptance of GRADE as well as building knowledge of the GRADE methodology in nutrition evidence synthesis.

Current Evidence Regarding Low-carb Diets for The Metabolic Control of Type-2 Diabetes

The management of diabetes requires a medical nutrition therapy as an essential part of this treatment. There should be no "one-size-fits-all" eating pattern for different patient´s profiles with diabetes. It is clinically complex to suggest an ideal percentage of calories from carbohydrates, protein and lipids recommended for all patients with diabetes. Among the eating patterns that have shown beneficial effects on metabolic control of patients with type 2 diabetes is the lowcarb diet, since the carbohydrate ingestion is viewed as the most important determinant of postprandial glucose and insulin response. In this context, theoretically, it could make sense to reduce the daily amount of carbohydrates ingested, to achieve lower levels of HbA1c. There could be risks associated to this approach. The adherence to a low-carb diet is here also discussed. This narrative review shows on the current evidence for answering these questions regarding low-carb diet as a possible alternative eating pattern for type 2 diabetes.

Lifestyle interventions for the prevention and treatment of hypertension

Hypertension affects approximately one third of the world's adult population and is a major cause of premature death despite considerable advances in pharmacological treatments. Growing evidence supports the use of lifestyle interventions for the prevention and adjuvant treatment of hypertension. In this Review, we provide a summary of the epidemiological research supporting the preventive and antihypertensive effects of major lifestyle interventions (regular physical exercise, body weight management and healthy dietary patterns), as well as other less traditional recommendations such as stress management and the promotion of adequate sleep patterns coupled with circadian entrainment. We also discuss the physiological mechanisms underlying the beneficial effects of these lifestyle interventions on hypertension, which include not only the prevention of traditional risk factors (such as obesity and insulin resistance) and improvements in vascular health through an improved redox and inflammatory status, but also reduced sympathetic overactivation and non-traditional mechanisms such as increased secretion of myokines.

Effect of Different Dietary Approaches in Comparison with High/Low-Carbohydrate Diets on Systolic and Diastolic Blood Pressure in Type 2 Diabetic Patients: A Systematic Review and Meta-Analysis

Dietary modification is an effective method for preventing and managing hypertension. Therefore, we conducted a systematic review and meta-analysis to assess the effects of different dietary approaches for comparing high- and low-carbohydrate diets on systolic and diastolic blood pressure (SBP and DBP, respectively) in patients with type 2 diabetes mellitus (T2DM). We carried out a comprehensive literature search using PubMed, the Cochrane Library, Web of Science, and Scopus without any language and time restrictions until April, 2019. We carried out a meta-analysis using both fixed and random effects models where appropriate and used the I2 index to evaluate heterogeneity. We identified 16 eligible studies, with a total of 1,610 participants. The overall pooled net effect of different dietary approaches on SBP and DBP were -2.29 mmHg [95% confidence interval (CI): -3.49 to -1.1] and -1.03 mmHg (95% CI: -1.77 to -0.29), respectively, compared with high-carbohydrate diets. Indeed, diets high in monounsaturated fatty acids more effective in reducing both SBP and DBP than high-carbohydrate diets, whereas high-protein diets were not effective. Furthermore, we found that different dietary approaches, such as low-fat diets, did not reduce SBP or DBP to a greater extent than low-carbohydrate diets. Overall, the results of our meta-analysis show that diets high in monounsaturated fatty acids are more effective in reducing both SBP and DBP than diets high in carbohydrate, whereas other dietary approaches were not effective.

Effects of Mediterranean diet supplemented with lean pork on blood pressure and markers of cardiovascular risk: findings from the MedPork trial

The Mediterranean diet offers a range of health benefits. However, previous studies indicate that the restricted consumption of red meat in the diet may affect long-term sustainability in non-Mediterranean countries. A 24-week randomised controlled parallel cross-over design compared a Mediterranean diet supplemented with 2–3 serves per week of fresh, lean pork (MedPork) with a low-fat control diet (LF). Thirty-three participants at risk of CVD followed each intervention for 8 weeks, with an 8-week washout period separating interventions. The primary outcome was home-measured systolic blood pressure. Secondary outcomes included diastolic blood pressure, fasting lipids, glucose, insulin, C-reactive protein (CRP), body composition and dietary adherence. During the MedPork intervention, participants achieved high adherence to dietary guidelines. Compared with the MedPork intervention, the LF intervention led to greater reductions in weight (Δ = −0·65; 95 % CI −0·04, −1·25 kg, P = 0·04), BMI (Δ = −0·25; 95 % CI −0·03, −0·47 kg/m2, P = 0·01) and waist circumference (Δ = −1·40; 95 % CI −0·45, −2·34 cm, P < 0·01). No significant differences were observed for blood pressure, lipids, glucose, insulin or CRP. These findings indicate that Australians are capable of adhering to a Mediterranean diet with 2–3 weekly serves of fresh, lean pork. Larger intervention studies are now required to demonstrate clinical efficacy of the diet in populations with elevated blood pressure.