Groundbreaking new research has revealed that swapping out carbohydrates for protein and fat in the diet can enhance cholesterol profiles among those with type 2 diabetes, and remarkably, these improvements occur independent of weight loss.
In a recently published study in The American Journal of Clinical Nutrition, a team of investigators set out to ascertain whether trimming dietary carbohydrates and upping the intake of protein and fat could better the lipoprotein subclass profiles in type 2 diabetes (T2D), irrespective of any alterations in body weight.
The Backdrop: Evolving Dietary Wisdom for T2D Management
Adopting a healthier lifestyle forms the bedrock of managing T2D, with weight loss frequently spotlighted. Conventional dietary advice has long leaned towards low-fat, high-carbohydrate regimens. Yet, emerging data indicates that cutting back on carbohydrate consumption might enhance glycemic control and mitigate diabetic dyslipidemia.
Carbohydrate restriction can normalize triacylglycerol (TAG) and High-density lipoprotein (HDL) cholesterol, though its impact on Low-density lipoprotein (LDL) cholesterol varies. It also holds the potential to alleviate metabolic dysfunction-associated steatotic liver disease (MASLD), though conclusive evidence remains elusive due to issues like poor compliance and confounding elements such as weight loss or exercise. Hence, further exploration is essential to untangle the stand-alone effects of carbohydrate curtailment on lipid metabolism.
Two studies were carried out as open-label, prospective, randomized controlled trials (RCTs) at Copenhagen University Hospital Bispebjerg. Their aim? To gauge the consequences of a carbohydrate-reduced high-protein (CRHP) diet against a conventional diabetes (CD) diet over a six-week span.
The Iso study incorporated a cross-over design, involving 30 participants who maintained a stable weight. Meanwhile, the Hypo study employed a parallel-group layout, with 72 participants striving for a 6% weight reduction. Both trials received the green light from the local ethics committee and adhered rigidly to strict eligibility benchmarks.
Individuals with T2D, with Hemoglobin A1c (HbA1c) levels ranging from 48 to 97 mmol/mol (6.5–11%), were enlisted. Exclusions were made for those with severe renal disease, anemia, critical illness, and specific medications.
The dietary intervention was meticulously planned. The CRHP meals were composed of 30% of energy (E%) from carbohydrates, 30 E% from protein, and 40 E% from fat. In contrast, the CD diet comprised 50 E% carbohydrates, 17 E% protein, and 33 E% fat.
All meals were expertly prepared and distributed by research staff to guarantee adherence. Participants were directed to consume only the provided victuals. Weight maintenance or loss was overseen in line with the study blueprint, and physical activity stayed at habitual levels.
Blood samples and lipoprotein profiling were conducted pre- and post-intervention, scrutinizing parameters like HbA1c, lipid concentrations, and insulin resistance. The intrahepatic triglyceride (IHTG) content was appraised via magnetic resonance spectroscopy. Sophisticated statistical analyses, including linear mixed models, were deployed to evaluate diet impacts and factor in body weight oscillations. Pearson’s analysis was used to assess correlations between changes in IHTG and lipid profiles.
In both studies, participant retention was impressively high, with a mere 7% dropping out post-randomization for reasons unconnected to trial outcomes or adverse incidents. The baseline traits of participants in the Iso and Hypo studies were largely comparable.
However, those in the Hypo study were more corpulent, had higher fasting insulin concentrations, and exhibited greater insulin resistance than their Iso study counterparts. In the Hypo study, baseline characteristics between dietary groups were mostly balanced, barring a higher proportion of men and participants using dipeptidyl peptidase-4 (DPP-4) inhibitors in the CRHP cohort.
Most participants had their dyslipidemia under reasonable control, with group mean concentrations of TAG, LDL cholesterol, and HDL cholesterol falling within normal parameters.
In the Iso study, body weight was successfully stabilized across both diet groups. But it was the CRHP diet that truly shone, significantly enhancing lipoprotein profiles compared to the CD diet. It slashed the atherogenic subfractions of TAG-rich lipoproteins (TRL) and LDL5 while elevating the HDL2/HDL3 ratio, signaling a shift towards a less atherogenic lipoprotein makeup.
In the Hypo study, where both groups achieved comparable weight loss, the CRHP diet displayed a propensity to reduce TRL. It notably diminished LDL5, augmented the HDL2/HDL3 ratio, and manifested a more pronounced improvement in IHTG than the CD diet.
Glucometabolic enhancements were witnessed in both studies. In the Iso study, the CRHP diet surpassed the CD diet in significantly reducing HbA1c, fasting TAG, and IHTG.
In the Hypo study, weight loss alone did improve these markers, but the CRHP diet amplified the benefits, cutting HbA1c and circulating TAG more effectively. Across both studies, the CRHP diet consistently outperformed the CD diet in reducing IHTG.
Correlations between shifts in IHTG and lipid parameters painted a consistent picture. In the Iso study, reductions in IHTG were tightly linked to enhancements in TAG, TRL, LDL5, and the HDL2/HDL3 ratio. Similar patterns emerged in the Hypo study, where changes in IHTG correlated with declines in TAG, TRL, and LDL5.
To sum it up, the study established that a CRHP diet could enhance plasma lipoprotein density profiles in T2D patients over a six-week period. Key transformations encompassed reductions in fasting TAG and small-dense LDL5 particles, along with an increased HDL2/HDL3 ratio compared to a CD diet. These effects were evident during both weight maintenance and loss phases.
Moreover, in the weight-maintenance scenario, the CRHP diet trimmed total cholesterol, non-HDL cholesterol, and Apolipoprotein B (ApoB) levels. The improvements were deeply intertwined with decreases in IHTG, intimating that liver fat depletion was pivotal.
While weight loss in both diet groups augmented lipid profiles, the CRHP diet proffered supplementary atheroprotective perks, underlining its potential as a targeted dietary intervention for T2D-linked dyslipidemia and metabolic malfunction.
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