Low-Carb vs Low-Fat Diets and Inflammation

Background

Dr. Cassandra Forsythe, Dr. Stephen Phinney, Dr. Maria Luz Fernandez and colleagues published this RCT in Lipids (PMID: 18046594, DOI: 10.1007/s11745-007-3132-7), comparing inflammatory marker responses to low-carbohydrate vs. low-fat diets.

Study Design

Design: Randomized controlled trial Population: 40 overweight/obese adults with metabolic syndrome features Groups:

• •Very low-carbohydrate ketogenic diet (VLCKD): <10% carb, ~60% fat
• •Low-fat diet (LFD): <30% fat, ~55% carb Duration: 12 weeks Endpoints: Inflammatory markers, fatty acid composition

Key Findings

Marker	VLCKD Change	LFD Change	P value
hsCRP	−29%	−3%	0.03
TNF-α	−32%	−4%	0.01
IL-6	−26%	+8%	0.02
Saturated fat in blood	↓ decreased	↔ unchanged	<0.05

Paradox: Despite consuming 3x more saturated fat, the VLCKD group had LOWER blood saturated fatty acids.

Mechanistic Insights

When carbohydrates are restricted:

1. •Dietary saturated fat is oxidized for energy, not stored
2. •De novo lipogenesis (carb→fat) stops
3. •Inflammation decreases as insulin falls
4. •Ketones have direct anti-inflammatory effects

Clinical Implications

This challenges the assumption that dietary fat increases inflammation. The metabolic context (carbohydrate status) determines how dietary fat is processed. Low-carb diets may be superior for reducing inflammation.

Metabolic Health Perspective

For patients with elevated inflammatory markers and insulin resistance, carbohydrate restriction may be more effective than fat restriction for reducing systemic inflammation.