14-Day Medically Supervised Fasting Cut Small, Dense LDL by 30%: What the Research Shows

14-Day Medically Supervised Fasting Cut Small, Dense LDL by 30%: 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

Researchers wanted to know what happens to the detailed subtypes of cholesterol-carrying particles in the blood — not just total LDL, but the specific size and density fractions that matter most for cardiovascular risk — during an extended, medically supervised fast. This matters because standard cholesterol panels report LDL as a single number, while the actual atherogenic risk depends heavily on particle size: small, dense LDL particles are far more likely to lodge in artery walls than larger, more buoyant ones. This connects to broader questions about how fasting affects the body long after the initial adjustment period and whether prolonged fasts offer cardiovascular benefits beyond simple weight loss.

Who Was Studied

Participant profile: Volunteers were aged 32–65, evenly split between men and women, and were medically screened and supervised throughout the fast at a dedicated fasting clinic. This was not a randomized trial with a separate control group — every participant underwent the same fasting protocol, and results were compared to each individual's own baseline.

How the fasting protocol worked in this study: Participants followed a medically supervised modified fast providing approximately 250 kcal per day (typically from small amounts of juice and honey, in the Buchinger-style fasting tradition), for 14 consecutive days. Lipid and lipoprotein levels were measured using ultracentrifugation and nuclear magnetic resonance (NMR) spectroscopy — more detailed methods than a standard blood lipid panel — allowing researchers to break LDL down into its individual subfractions by size and density.

What the Researchers Found

LDL Particle Subfractions

• The reduction was not uniform across LDL particle types — the fast disproportionately reduced the small, dense LDL particles most strongly linked to arterial plaque formation
• Triglycerides, VLDL-triglycerides, and VLDL-cholesterol all decreased significantly over the 14-day fast
• The standout finding: fasting shifted the overall LDL profile toward a less atherogenic pattern, not just a lower total LDL number

What Did Not Change

• Apolipoprotein B (apoB), the structural protein found on every LDL and VLDL particle and a key marker of total atherogenic particle count, was unchanged
• Lipoprotein(a) — a genetically determined, largely diet-resistant risk marker — was unchanged
• Fibrinogen and high-sensitivity C-reactive protein (hs-CRP), both inflammation and clotting-related markers, were unchanged

What the Researchers Concluded

The authors concluded that a medically supervised 14-day fast shifts LDL cholesterol toward a smaller, less atherogenic particle profile and reduces triglyceride-rich lipoproteins, even though the total number of atherogenic particles (reflected by apoB) and genetically fixed markers like Lp(a) remain unchanged.

What This Means If You Fast

• Not all LDL reduction is equal. This study suggests fasting may preferentially reduce the small, dense LDL particles considered most dangerous for artery health, rather than simply lowering the total LDL number — a distinction standard cholesterol panels don't capture.
• Don't expect fasting to change your Lp(a). If you have elevated lipoprotein(a), a fasting protocol like this one is unlikely to move that specific number, since it appears largely resistant to dietary and fasting interventions.
• This was a prolonged fast, not a daily eating window. These results come from a supervised 14-day modified fast, not everyday 16:8 or 18:6 intermittent fasting — the magnitude of change seen here shouldn't be assumed to apply to shorter daily fasting patterns.
• Medical supervision mattered in this study. A 14-day fast at ~250 kcal/day is a significant intervention; the participants here were medically screened and monitored throughout, which is not a substitute for attempting something similar without guidance.
• This adds to a broader pattern of fasting research on cardiovascular markers showing improvements in triglycerides and lipid subfractions across various fasting protocols and durations.

Study Limitations

• No control group — all 40 participants underwent the same fasting protocol, so changes are compared to each person's own baseline rather than to a non-fasting comparison group
• Sample size was modest (n=40)
• The 14-day supervised fasting protocol is not directly comparable to shorter, more common intermittent fasting patterns
• Funding source was not reported in available summaries
• Long-term durability of the LDL subfraction changes after participants resumed normal eating was not assessed in this phase of the study
• As a single-arm study conducted at a specialized fasting clinic, findings may not generalize to unsupervised fasting in a general population

Source

Grundler F, Plonné D, Mesnage R, Müller D, Sirtori CR, Ruscica M, Wilhelmi de Toledo F. Long-term fasting improves lipoprotein-associated atherogenic risk in humans. European Journal of Nutrition. 2021;60(7):4031-4044. PMID: 33934216

Frequently Asked Questions

Does fasting lower LDL cholesterol?

Yes — this study found total LDL-cholesterol dropped by 0.72 mmol/L over a 14-day supervised fast, with the largest relative reduction (30%) in the small, dense LDL particles considered most atherogenic.

Does intermittent fasting reduce lipoprotein(a) (Lp(a))?

Not based on this study. Lp(a) is largely determined by genetics and was unchanged after the 14-day fast, consistent with other research showing Lp(a) is resistant to most dietary and lifestyle interventions.

What is small, dense LDL and why does it matter?

Small, dense LDL particles (sometimes called LDL3) are considered more likely than larger LDL particles to penetrate artery walls and contribute to plaque formation, making them a more specific marker of cardiovascular risk than total LDL alone.

Is a 14-day fast the same as intermittent fasting?

No. This study used a medically supervised, near-continuous 14-day fast providing only about 250 calories per day — a prolonged fasting protocol, distinct from daily intermittent fasting patterns like 16:8.

Did apolipoprotein B (apoB) improve with fasting in this study?

No — apoB, which reflects the total number of atherogenic particles in the blood, was unchanged, even though LDL cholesterol and the proportion of small, dense particles improved.

Related Research and Articles

• Fasting and inflammation: what women should know
• Extended Fasting (5+ Days): What to Expect and How to Prepare
• How a 12-Day Fast Feels Day by Day
• What Happens in Your Body When You Stop Eating for 12 Hours
• Is a 7-Day Fast Safe? What Historical Cases Tell Us

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