Alternate Day Fasting Shifts LDL to Safer, Larger Particles — Even Without Calorie Counting: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Most discussions about fasting and heart health focus on LDL cholesterol as a single number — the lower, the better. But cardiologists have known for decades that the size and density of LDL particles matters as much as, or more than, the total count. Small, dense LDL particles are far more atherogenic than larger, buoyant ones: they penetrate arterial walls more easily and are more susceptible to oxidation, making them the particles most strongly linked to plaque formation and cardiovascular risk.

This study asked whether alternate day modified fasting (ADMF) — a pattern where participants eat only 25% of their normal calorie intake every other day — could not only reduce LDL cholesterol, but specifically shift the LDL particle population toward the larger, less dangerous type. It builds on earlier ADF work on body weight and standard lipid markers, bringing the more clinically relevant question of particle size into the picture for the first time. You can read more about what the research shows on intermittent fasting and inflammation and how fasting affects cardiovascular markers generally.

Who Was Studied

Participant profile: 16 obese adults. Mean body weight at baseline not specified in the abstract. Inclusion criteria required obesity (BMI ≥ 30 kg/m²). Participants were otherwise generally healthy.

How alternate day modified fasting worked in this study: Every other day ("fast day"), participants consumed approximately 25% of their estimated daily calorie needs — roughly 500 kcal for women and 600 kcal for men. On "feast days," they ate freely with no restrictions. The controlled feeding phase provided weighed, prepared meals to ensure precision; the self-selected phase gave participants the same protocol but let them choose their own food, testing whether the effects held outside a controlled setting.

What the Researchers Found

LDL Particle Size and Distribution

The study's most clinically significant finding was not just a reduction in LDL cholesterol, but a measurable improvement in the character of the remaining particles.

All changes were statistically significant (P < 0.05). The proportion of large LDL particles increased from 68% to 76% of the total LDL pool — a meaningful shift toward the less atherogenic phenotype.

Standard Lipid Panel Changes

Both reductions were statistically significant (P < 0.05).

Body Composition Changes

• Body weight decreased by 5.6 (±0.9) kg — a reduction of roughly 5–6% of body weight
• Waist circumference decreased by 4.0 (±0.9) cm

Both changes were statistically significant (P < 0.05).

What Did Not Change

• The study focused on LDL particle size and basic lipid/body composition outcomes; HDL cholesterol, fasting glucose, blood pressure, and inflammatory markers were not reported as primary outcomes in this investigation

What the Researchers Concluded

The researchers concluded that alternate day modified fasting produced favourable changes in LDL particle size and distribution in obese adults, independent of the dietary fat composition consumed on feast days. The dual benefit — reducing total LDL-C by 25% and shifting particles toward a less atherogenic profile — suggests that the fasting pattern itself, rather than specific macronutrient adjustments, drives the cardiovascular benefit.

What This Means If You Fast

• LDL-C alone does not tell the full cardiovascular story. A reduction in LDL particle count is important, but moving more of the remaining particles into the larger, buoyant category is arguably more important for lowering actual cardiovascular risk. This study documents both.

• You don't need to follow a low-fat diet to improve your lipids through fasting. When the researchers later compared high-fat and low-fat ADF diets (Klempel et al., 2013), both improved LDL particle size equally. The fasting pattern does the work, not the macronutrient split.

• The effect appeared across both controlled and self-selected feeding. The results held even when participants chose their own food during feast days — which makes this finding more practically relevant. You don't need a rigid meal plan alongside the fasting.

• Weight loss may not be the sole mechanism. The 5.6 kg of weight lost over 8 weeks likely contributed, but the LDL particle shift may also reflect direct metabolic effects of cyclical fasting — including reduced post-prandial lipemia on fast days and improved insulin sensitivity.

• For people with elevated small-dense LDL ("atherogenic dyslipidemia"), fasting deserves serious consideration. This pattern — high triglycerides, elevated small dense LDL, low HDL — is extremely common in metabolic syndrome and is not reliably corrected by standard dietary advice. Alternate day fasting may be one of the more targeted dietary interventions for this specific lipid phenotype.

• The reduction in triglycerides (-32%) is clinically meaningful on its own. Fasting triglycerides above 150 mg/dL are an independent cardiovascular risk factor and are strongly linked to insulin resistance. A 32% reduction in 8 weeks without calorie counting is a clinically significant outcome. See also how intermittent fasting compares to calorie counting for context.

Study Limitations

• Very small sample size. Sixteen participants is insufficient to draw firm conclusions about effect sizes or population generalisability. This is best viewed as a proof-of-concept pilot study.
• No parallel control group. The 2-week control phase provides a within-subjects baseline, but without a contemporaneous control group eating ad libitum for the full 10 weeks, the study cannot definitively rule out seasonal or other time-related confounders.
• Gender distribution not specified in the abstract, limiting interpretation for sex-specific effects.
• Short duration. Eight weeks captures initial adaptation but not long-term maintenance. Whether LDL particle improvements are sustained over 6–12 months is unknown from this study.
• Self-selected phase nutritional data. What participants actually ate on feast days during the self-selected phase was not fully characterised, making it difficult to attribute the effect precisely to the fasting pattern alone vs. spontaneous dietary changes.
• Funding not reported. No conflicts of interest were noted in the available abstract.

Source

Varady KA, Bhutani S, Klempel MC, Lamarche B. (2011). Improvements in LDL particle size and distribution by short-term alternate day modified fasting in obese adults. British Journal of Nutrition, 105(4), 580–583. PMID: 20880415

Frequently Asked Questions

Does intermittent fasting reduce LDL cholesterol?

This study found LDL cholesterol fell by an average of 25% over 8 weeks of alternate day modified fasting in obese adults. That is a substantial reduction, comparable to what is seen with moderate statin therapy in some populations. The effect may be smaller in people who are not obese or who already eat relatively cleanly.

What is LDL particle size and why does it matter?

LDL particles vary in size: larger, more buoyant particles are less likely to penetrate arterial walls and are less prone to oxidation. Smaller, denser LDL particles are more atherogenic — they are the fraction most closely associated with coronary artery disease risk. This study measured particle size directly using gradient gel electrophoresis, which provides more clinical detail than standard LDL-C measurement.

What is alternate day modified fasting (ADMF)?

In ADMF, you alternate between fast days — where you consume approximately 25% of your normal calorie intake (roughly 500–600 kcal) — and unrestricted feast days. This differs from a traditional 16:8 or 18:6 protocol in that the restriction is calorie-based rather than time-window-based. The studies from this group typically use a structured meal plan on fast days (usually a single midday meal).

Is the improvement in LDL particle size due to weight loss or fasting specifically?

This study cannot fully separate the two. The 5.6 kg weight loss likely contributed to the lipid improvements. However, a separate study from the same research group found that both high-fat and low-fat ADF diets produced equivalent LDL particle improvements — suggesting the pattern of eating (alternate-day restriction) rather than the dietary composition drives the effect, which implies fasting-specific mechanisms beyond simple caloric restriction.

Should I switch to alternate day fasting to improve my cholesterol?

This study was a small pilot in 16 obese adults, so it cannot be generalised broadly. If you have elevated LDL or atherogenic dyslipidemia (high triglycerides, high small-dense LDL, low HDL), this research is promising but should be discussed with your doctor before making changes to any medication or diet. ADF can also lower blood pressure and blood sugar, which may require adjustment of existing medications.

Related Research and Articles

• Intermittent fasting benefits: the complete science-backed guide
• What is alternate day fasting and does it work?
• Does intermittent fasting help with high cholesterol?
• Intermittent fasting and inflammation: the research explained
• How intermittent fasting compares to calorie counting
• Intermittent fasting and metabolism: what science says
• Can intermittent fasting improve insulin sensitivity?

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