The Effect of Dietary Interventions on Hypertriglyceridemia: From Public Health to Molecular Nutrition Evidence

Approximately 25–50% of the population worldwide exhibits serum triglycerides (TG) (≥150 mg/dL) which are associated with an increased level of highly atherogenic remnant-like particles, non-alcoholic fatty liver disease, and pancreatitis risk. High serum TG levels could be related to cardiovascular disease, which is the most prevalent cause of mortality in Western countries. The etiology of hypertriglyceridemia (HTG) is multifactorial and can be classified as primary and secondary causes. Among the primary causes are genetic disorders. On the other hand, secondary causes of HTG comprise lifestyle factors, medical conditions, and drugs. Among lifestyle changes, adequate diets and nutrition are the initial steps to treat and prevent serum lipid alterations. Dietary intervention for HTG is recommended in order to modify the amount of macronutrients. Macronutrient distribution changes such as fat or protein, low-carbohydrate diets, and caloric restriction seem to be effective strategies in reducing TG levels. Particularly, the Mediterranean diet is the dietary pattern with the most consistent evidence for efficacy in HTG while the use of omega-3 supplements consumption is the dietary component with the highest number of randomized clinical trials (RCT) carried out with effective results on reducing TG. The aim of this review was to provide a better comprehension between human nutrition and lipid metabolism.

Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk

BACKGROUND

Debates on effective and safe diets for managing obesity in adults are ongoing. Low-carbohydrate weight-reducing diets (also known as 'low-carb diets') continue to be widely promoted, marketed and commercialised as being more effective for weight loss, and healthier, than 'balanced'-carbohydrate weight-reducing diets.

OBJECTIVES

To compare the effects of low-carbohydrate weight-reducing diets to weight-reducing diets with balanced ranges of carbohydrates, in relation to changes in weight and cardiovascular risk, in overweight and obese adults without and with type 2 diabetes mellitus (T2DM).

SEARCH METHODS

We searched MEDLINE (PubMed), Embase (Ovid), the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science Core Collection (Clarivate Analytics), ClinicalTrials.gov and WHO International Clinical Trials Registry Platform (ICTRP) up to 25 June 2021, and screened reference lists of included trials and relevant systematic reviews. Language or publication restrictions were not applied.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in adults (18 years+) who were overweight or living with obesity, without or with T2DM, and without or with cardiovascular conditions or risk factors. Trials had to compare low-carbohydrate weight-reducing diets to balanced-carbohydrate (45% to 65% of total energy (TE)) weight-reducing diets, have a weight-reducing phase of 2 weeks or longer and be explicitly implemented for the primary purpose of reducing weight, with or without advice to restrict energy intake.  DATA COLLECTION AND ANALYSIS: Two review authors independently screened titles and abstracts and full-text articles to determine eligibility; and independently extracted data, assessed risk of bias using RoB 2 and assessed the certainty of the evidence using GRADE. We stratified analyses by participants without and with T2DM, and by diets with weight-reducing phases only and those with weight-reducing phases followed by weight-maintenance phases. Primary outcomes were change in body weight (kg) and the number of participants per group with weight loss of at least 5%, assessed at short- (three months to < 12 months) and long-term (≥ 12 months) follow-up.

MAIN RESULTS

We included 61 parallel-arm RCTs that randomised 6925 participants to either low-carbohydrate or balanced-carbohydrate weight-reducing diets. All trials were conducted in high-income countries except for one in China. Most participants (n = 5118 randomised) did not have T2DM. Mean baseline weight across trials was 95 kg (range 66 to 132 kg). Participants with T2DM were older (mean 57 years, range 50 to 65) than those without T2DM (mean 45 years, range 22 to 62). Most trials included men and women (42/61; 3/19 men only; 16/19 women only), and people without baseline cardiovascular conditions, risk factors or events (36/61). Mean baseline diastolic blood pressure (DBP) and low-density lipoprotein (LDL) cholesterol across trials were within normal ranges. The longest weight-reducing phase of diets was two years in participants without and with T2DM. Evidence from studies with weight-reducing phases followed by weight-maintenance phases was limited. Most trials investigated low-carbohydrate diets (> 50 g to 150 g per day or < 45% of TE; n = 42), followed by very low (≤ 50 g per day or < 10% of TE; n = 14), and then incremental increases from very low to low (n = 5). The most common diets compared were low-carbohydrate, balanced-fat (20 to 35% of TE) and high-protein (> 20% of TE) treatment diets versus control diets balanced for the three macronutrients (24/61). In most trials (45/61) the energy prescription or approach used to restrict energy intake was similar in both groups. We assessed the overall risk of bias of outcomes across trials as predominantly high, mostly from bias due to missing outcome data. Using GRADE, we assessed the certainty of evidence as moderate to very low across outcomes.  Participants without and with T2DM lost weight when following weight-reducing phases of both diets at the short (range: 12.2 to 0.33 kg) and long term (range: 13.1 to 1.7 kg).  In overweight and obese participants without T2DM: low-carbohydrate weight-reducing diets compared to balanced-carbohydrate weight-reducing diets (weight-reducing phases only) probably result in little to no difference in change in body weight over three to 8.5 months (mean difference (MD) -1.07 kg, (95% confidence interval (CI) -1.55 to -0.59, I2 = 51%, 3286 participants, 37 RCTs, moderate-certainty evidence) and over one to two years (MD -0.93 kg, 95% CI -1.81 to -0.04, I2 = 40%, 1805 participants, 14 RCTs, moderate-certainty evidence); as well as change in DBP and LDL cholesterol over one to two years. The evidence is very uncertain about whether there is a difference in the number of participants per group with weight loss of at least 5% at one year (risk ratio (RR) 1.11, 95% CI 0.94 to 1.31, I2 = 17%, 137 participants, 2 RCTs, very low-certainty evidence).  In overweight and obese participants with T2DM: low-carbohydrate weight-reducing diets compared to balanced-carbohydrate weight-reducing diets (weight-reducing phases only) probably result in little to no difference in change in body weight over three to six months (MD -1.26 kg, 95% CI -2.44 to -0.09, I2 = 47%, 1114 participants, 14 RCTs, moderate-certainty evidence) and over one to two years (MD -0.33 kg, 95% CI -2.13 to 1.46, I2 = 10%, 813 participants, 7 RCTs, moderate-certainty evidence); as well in change in DBP, HbA1c and LDL cholesterol over 1 to 2 years. The evidence is very uncertain about whether there is a difference in the number of participants per group with weight loss of at least 5% at one to two years (RR 0.90, 95% CI 0.68 to 1.20, I2 = 0%, 106 participants, 2 RCTs, very low-certainty evidence).  Evidence on participant-reported adverse effects was limited, and we could not draw any conclusions about these.  AUTHORS' CONCLUSIONS: There is probably little to no difference in weight reduction and changes in cardiovascular risk factors up to two years' follow-up, when overweight and obese participants without and with T2DM are randomised to either low-carbohydrate or balanced-carbohydrate weight-reducing diets.

[Effect of a Mediterranean-pattern diet on the metabolic response secondary to weight loss; role of the single nucleotide polymorphism (rs16147) of neuropeptide Y]

Introduction

Background and aims: intervention studies that evaluate the effect of rs16147 on metabolic response and weight change after dietary intervention are scarce. We propose to evaluate the role of the rs16147 genetic variant in the metabolic effects produced by a hypocaloric Mediterranean-pattern diet with high content of omega-9. Material and methods: a sample of 363 obese subjects was recruited. At the baseline visit the patients were randomly assigned to one of two hypocaloric diets for 12 weeks (diet M, Mediterranean pattern; diet C, standard hypocaloric). All patients, at baseline and at 12 weeks, had biochemical and anthropometric variables measured, and genotyping performed for the rs16147 variant. Results: in all subjects, and with both diets, the parameters of adiposity, blood pressure, and circulating leptin improved. In obese subjects with allele (A) insulin levels (GG vs. GA + AA) (-0.9 ± 1.1 IU/L vs. -4.4 ± 1.0 IU/L; p = 0.01) and HOMA-IR (-0.3 ± 0.1 units vs. -1.2 ± 0.3 units; p = 0.02) decreased significantly with diet M. Subjects carrying the minor allele showed a significant decrease in basal insulin levels (GG vs. GA + AA) (0.7 ± 0.3 IU/L vs. -2.2 ± 0.9 IU/L: p = 0.02) and HOMA-IR (-0.3 ± 0.2 units vs. -0.7 ± 0.1 units: p = 0.01) after diet C. This decrease in circulating insulin and HOMA-IR levels in patients with allele A was significantly higher with diet M than with diet C. Conclusions: the A allele of the rs16147 variant produces a better metabolic response in terms of insulin resistance and basal insulin secondary to weight loss with two different hypocaloric diets in obese subjects, with improvement being higher with the Mediterranean diet.

Different effects of high-protein/low-carbohydrate versus standard hypocaloric diet on insulin resistance and lipid profile: Role of rs16147 variant of neuropeptide Y

BACKGROUND AND AIMS

Few studies have assessed the effect of the NPY gene rs16147 variant on metabolic response following a dietary intervention. We evaluated the effect of rs16147 on body weight and biochemical changes after a high-protein/low-carbohydrate hypocaloric diet compared with a standard severe hypocaloric diet over 9 months.

MATERIALS AND METHODS

A population of 270 obese individuals was enrolled. At baseline, participants were randomly allocated to one of two hypocaloric diets, high protein (Diet HP) or standard (Diet S), for a period of 9 months.

RESULTS

After both diets, all genotypes showed decreased body mass index, weight, fat mass, waist circumference, and leptin levels. Participants with the minor allele (A) assigned to the HP diet showed decreases in total cholesterol (-6.5 ± 4.8 vs 10.1 ± 4.1 mg/dL; p < 0.05), LDL cholesterol (-5.9 ± 3.8 vs 9.6 ± 2.4 mg/dL; p < 0.05), triglycerides (-1.0 ± 4.8 vs 16.2 ± 4.1 mg/dL; p < 0.05), insulin (-0.5 ± 2.8 vs 1.7 ± 2.1 UI/L; p < 0.05), HOMA-IR (-0.2 ± 2.1 vs 0.5 ± 2.0 units; p < 0.05), and CRP (-0.3 ± 0.4 vs 1.3 ± 0.2 mg/dL; p < 0.05). Participants with the minor allele assigned to diet S also showed decreases in total cholesterol (-6.1 ± 4.1 vs 14.4 ± 3.1 mg/dL; p < 0.05), LDL-cholesterol (-3.1 ± 2.8 vs 15.0 ± 3.1 mg/dL; p < 0.05), triglycerides (-6.9 ± 4.1 vs 13.2 ± 4.0 mg/dL; p < 0.05), insulin (-0.3 ± 2.1 vs. -1.2 ± 0.2 UI/L: p < 0.05), HOMA-IR (-0.3 ± 2.1 vs. -1.6 ± 1.1 units: p < 0.05), and CRP (-0.4 ± 0.1 vs 1.1 ± 0.2 mg/dL; p < 0.05).

CONCLUSION

In obese Caucasians, the presence of the A allele of the rs16147 genetic variant produces a better metabolic response that is secondary to weight loss with two different hypocaloric diets.

Role of neuropeptide Y gene variant (rs161477) in liver histology in obese patients with non-alcoholic fatty liver disease

BACKGROUND AND RATIONALE

This study was intended to assess the influence of the rs16147 variant of the NPY gene on liver histology in patients with non-alcoholic fatty liver disease (NAFLD).

MATERIAL AND METHODS

Eighty-nine patients with NAFLD were recruited into the study. Serum chemistry tests were done including lipid profile, transaminases, adipokines, and insulin resistance. Genotype of polymorphism (rs161477) of the NPY gene was studied.

RESULTS

Twenty-three patients (25.0%) had the GG genotype (wild type) and sixty-six patients (75%) the GA (n=39) or AA (n=27) (mutant) types. Patients with A allele had a lower percentage of lobular inflammation and steatohepatitis (lobular inflammation plus ballooning) than those with wild genotype. Patients with A allele showed lower SAF (Steatosis, Activity, Fibrosis) scores than non-A allele carriers (5.4±2.7 points vs. 4.1±1.1 points; p=0.01). In the analysis without fibrosis (NAS score), the same differences were detected (4.5±1.8 points vs. 3.4±1.8 points; p=0.01). In the logistic regression analysis A allele carriers showed lower odds for inflammation (OR 0.11, 95% CI 0.02-0.84, p=0.03) and steatohepatitis (OR 0.39, 95% CI 0.14-0.86, p=0.04) after adjusting for age, sex, and body mass index.

CONCLUSIONS

A variant of polymorphism rs16147 of the NPY gene is independently associated to a lower percentage of steatohepatitis and lobular inflammation in obese subjects with biopsy-proven NAFLD.