Baseline Insulin Resistance Is a Determinant of the Small, Dense Low-Density Lipoprotein Response to Diets Differing in Saturated Fat, Protein, and Carbohydrate Contents

Evaluating the differential benefits of varying carbohydrate-restricted diets on lipid profiles and cardiovascular risks in dyslipidemia: a meta-analysis and systematic review

Background: carbohydrate-restricted diets (CRDs) have gained attention to address metabolic dysregulation commonly observed in dyslipidemia, a condition posing significant risks to cardiovascular health. However, the effectiveness of CRDs in improving cardiovascular health remains contentious. This meta-analysis comprehensively evaluated the long-term effects of CRDs on glucolipid metabolism and weight loss in individuals with dyslipidemia. Methods: extensive searches were conducted in PubMed, Web of Science, Scopus, the Cochrane Library, and EMBASE. Randomized controlled trials examining the effects of CRDs on glucolipid metabolism and weight loss in adults with dyslipidemia over a minimum of three weeks were included. This analysis compared the differential effects between moderate-low carbohydrate diets (MLCDs) and low carbohydrate diets (LCDs), including a targeted evaluation of animal-based CRDs and dyslipidemic individuals based on the BMI status, thereby addressing gaps in current knowledge. Results: Our findings indicated that CRDs significantly enhanced lipid profiles, including total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and apolipoprotein B (ApoB), and contributed to weight management in individuals with dyslipidemia. MLCDs were more effective than LCDs in improving all lipid profiles except for TG, which was more effectively managed by LCDs. Animal-based CRDs did not significantly impact lipid profiles. Dyslipidemic individuals with overweight and obesity showed significant changes in TG and ApoB. A noteworthy negative correlation was also observed between TC, TG, and low-density lipoprotein cholesterol levels with higher dietary fiber intake, supporting the beneficial impact of fiber on cardiovascular health. Conclusions: These results for the first time highlighted the potential of adopting MLCDs, particularly those with sufficient fiber content, as a powerful strategy for reducing the risk of cardiovascular diseases in patients suffering from dyslipidemia.

Replacing dietary carbohydrate with protein and fat improves lipoprotein subclass profile and liver fat in type 2 diabetes independent of body weight: evidence from 2 randomized controlled trials

BACKGROUND

Dyslipidemia with elevated concentrations of triacylglycerol-rich lipoproteins (TRLs), small-dense LDL, and reduced HDL is linked to hepatic steatosis and promotes atherogenesis in type 2 diabetes (T2D).

OBJECTIVES

We aimed to analyze whether moderate carbohydrate restriction reduces liver fat in T2D independent of changes in body weight and whether this is accompanied by parallel improvements in plasma lipoprotein subclasses.

METHODS

We determined the density profile of circulating lipoproteins in patients with T2D from 2 previous randomized controlled trials. In the isoenergetic study, 30 participants were allocated in a crossover design to 6 + 6 wk of an isocaloric carbohydrate-reduced high-protein (CRHP, C/P/F = 30/30/40 E%) or conventional diabetes (CD, C/P/F = 50/17/33 E%) diet aimed at weight maintenance. In the hypoenergetic study, 72 participants were allocated in a parallel-group design to 6 wk of a hypocaloric CRHP or CD diet aimed at matched ∼6% weight loss. Both studies provided all meals from a metabolic kitchen to maximize adherence.

RESULTS

In the isoenergetic study, the CRHP diet reduced TRL (mean: -33%; 95% CI: -48%, -14%) and LDL5 (mean: -16%; 95% CI: -26%, -4%) and increased HDL2/HDL3 (mean: 10%; 95% CI: 0%, 22%) compared with the CD diet. In the hypoenergetic study, weight loss induced by CRHP diet tended to reduce TRL (mean: -16%; 95% CI: -30%, 1%), reduced LDL5 (mean: -13%; 95% CI: -22%, -3%), and increased HDL2/HDL3 (mean: 11%; 95% CI: 1%, 22%) compared with an equivalent weight loss induced by CD diet. The CRHP diet decreased intrahepatic triacylglycerol (IHTG) more than the CD diet (isoenergetic: -55%; 95% CI: -74%, -22%; hypoenergetic: -26%; 95% CI: -45%, 0%), and changes in IHTG correlated directly with changes in TRL and LDL5 (r = 0.36-0.55; P < 0.01 for all) in both studies.

CONCLUSIONS

Replacing dietary carbohydrate with protein and fat improves dyslipidemia in T2D independently of changes in body weight, by inducing an atheroprotective shift in the lipoprotein particle profile possibly facilitated by reduced IHTG accumulation. These trials were registered at clinicaltrials.gov as NCT02764021 (https://clinicaltrials.gov/study/NCT02764021?term=NCT02764021&rank=1) and NCT03814694 (https://clinicaltrials.gov/study/NCT03814694?term=NCT03814694&rank=1).

Healthy Dietary Patterns with and without Meat Improved Cardiometabolic Disease Risk Factors in Adults: A Randomized Crossover Controlled Feeding Trial

We assessed the effects of consuming a U.S.-style healthy dietary pattern (HDP) with lean, unprocessed beef (BEEF) compared to a U.S.-style HDP without meat (vegetarian, VEG) on short-term changes in cardiometabolic disease (CMD) risk factors in adults classified as overweight or obese. Forty-one adults (22 females, 19 males; age 39.9 ± 8.0 y; BMI 29.6 ± 3.3 kg/m2; mean ± SD) completed two 5-week controlled feeding periods (randomized, crossover, controlled trial). For the BEEF HDP, two 3-oz (168-g) servings/d of lean, unprocessed beef were predominately substituted for some starchy vegetables and refined grains in the VEG HDP. Baseline and post-intervention measurements were fasting CMD risk factors, with serum low-density lipoprotein (LDL), total cholesterol (TC), and total apolipoprotein B as primary outcomes. VEG reduced LDL, insulin, and glucose compared to BEEF. Reductions did not differ between VEG vs. BEEF for TC, high-density lipoprotein (HDL), apolipoprotein A1, small, dense LDL IV, buoyant HDL2b, TC-to-HDL ratio, and systolic blood pressure. Total apolipoprotein B and all other CMD risk factors measured were not influenced by HDP type nor changed over time. Adopting a U.S.-style HDP that is either vegetarian or omnivorous with beef improved multiple cardiometabolic disease risk factors among adults classified as overweight or obese.

Separation of Lipoproteins for Quantitative Analysis of 14C-Labeled Lipid-Soluble Compounds by Accelerator Mass Spectrometry

To date, 14C tracer studies using accelerator mass spectrometry (AMS) have not yet resolved lipid-soluble analytes into individual lipoprotein density subclasses. The objective of this work was to develop a reliable method for lipoprotein separation and quantitative recovery for biokinetic modeling purposes. The novel method developed provides the means for use of small volumes (10-200 µL) of frozen plasma as a starting material for continuous isopycnic lipoprotein separation within a carbon- and pH-stable analyte matrix, which, following post-separation fraction clean up, created samples suitable for highly accurate 14C/12C isotope ratio determinations by AMS. Manual aspiration achieved 99.2 ± 0.41% recovery of [5-14CH3]-(2R, 4'R, 8'R)-α-tocopherol contained within 25 µL plasma recovered in triacylglycerol rich lipoproteins (TRL = Chylomicrons + VLDL), LDL, HDL, and infranatant (INF) from each of 10 different sampling times for one male and one female subject, n = 20 total samples. Small sample volumes of previously frozen plasma and high analyte recoveries make this an attractive method for AMS studies using newer, smaller footprint AMS equipment to develop genuine tracer analyses of lipophilic nutrients or compounds in all human age ranges.

Fitm2 is required for ER homeostasis and normal function of murine liver

The endoplasmic reticulum (ER)-resident protein fat storage-inducing transmembrane protein 2 (FIT2) catalyzes acyl-CoA cleavage in vitro and is required for ER homeostasis and normal lipid storage in cells. The gene encoding FIT2 is essential for the viability of mice and worms. Whether FIT2 acts as an acyl-CoA diphosphatase in vivo and how this activity affects the liver, where the protein was discovered, are unknown. Here, we report that hepatocyte-specific Fitm2 knockout (FIT2-LKO) mice fed a chow diet exhibited elevated acyl-CoA levels, ER stress, and signs of liver injury. These mice also had more triglycerides in their livers than control littermates due, in part, to impaired secretion of triglyceride-rich lipoproteins and reduced capacity for fatty acid oxidation. We found that challenging FIT2-LKO mice with a high-fat diet worsened hepatic ER stress and liver injury but unexpectedly reversed the steatosis phenotype, similar to what is observed in FIT2-deficient cells loaded with fatty acids. Our findings support the model that FIT2 acts as an acyl-CoA diphosphatase in vivo and is crucial for normal hepatocyte function and ER homeostasis in the murine liver.

Consuming High-Fat and Low-Fat Ground Beef Depresses High-Density and Low-Density Lipoprotein Cholesterol Concentrations, and Reduces Small, Dense Low-Density Lipoprotein Particle Abundance

We hypothesized that consumption of high-fat (HF) ground beef (24% fat) would not affect plasma concentrations of high-density lipoprotein cholesterol (HDL-C) or low-density lipoprotein (LDL-C), whereas low-fat (LF) ground beef (5% fat) would decrease HDL-C and LDL-C concentrations. In a randomized 2-period crossover, controlled feeding trial, 25 men (mean age and body mass index, 40 years and 31.2) consumed 115-g HF or LF patties, 5/week for 5 weeks with a 4-week washout. The HF treatment increased % energy from fat (p = 0.006) and saturated fat (p = 0.004) and tended (p = 0.060) to depress % energy from carbohydrates. The HF and LF treatments decreased the plasma concentrations of HDL-C (p = 0.001) and LDL-C (p = 0.011). Both ground beef treatments decreased the abundance of HDL3a and increased the abundance of HDL3 (p ≤ 0.003); the LF treatment also decreased the abundance of HDL2b and HDL2a (p ≤ 0.012). The HF and LF treatments decreased the abundance of LDL3 and LDL4 (p ≤ 0.024) and the HF treatment also decreased LDL5 (p = 0.041). Contrary to our hypothesis, the HF treatment decreased plasma HDL-C and LDL-C concentrations despite increased saturated fat intake, and both treatments decreased the abundance of smaller, denser LDL subfractions.

Eating Habits and Disease Risk Factors

Diet plays an inevitable role in human health and disease prevention [...]