Alternate Day Fasting Cuts LDL by 25% and Triglycerides by 32% in 8 Weeks: 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 at the University of Illinois at Chicago wanted to know whether alternate day modified fasting (ADMF) — a pattern where people restrict calories to about 25% of their needs every other day — could produce meaningful changes in body weight and cardiovascular risk markers in obese adults over a short period. The study was one of the first to systematically test this specific fasting pattern in a controlled setting, asking not just whether people lost weight but whether their heart health markers improved. This is relevant to anyone interested in whether intermittent fasting can lower cholesterol or reduce cardiovascular risk through dietary change.

Who Was Studied

Participant profile: Adults with obesity (BMI 30–39.9 kg/m²), aged 35–65, including both men and women. Participants were weight-stable for at least 3 months before enrolment, did not take lipid-lowering medications, and were free from cardiovascular or metabolic disease at baseline.

How alternate day modified fasting worked in this study: On fast days, participants consumed approximately 25% of their estimated energy needs (roughly 400–600 kcal depending on body size), eating a single provided meal at noon. On feast days, they were permitted to eat freely, with an estimated intake at approximately 125% of energy needs. This produced an overall weekly caloric deficit of around 37.5% compared to normal intake, without any requirement to count calories on feast days.

What the Researchers Found

Body Weight and Composition

• Body weight fell by an average of 6 kg over 8 weeks without any requirement to count calories on feast days
• Fat mass dropped by nearly 17% while lean muscle mass was maintained — a particularly important finding, since most weight loss approaches that restrict calories significantly cause muscle loss alongside fat loss
• The reduction in fat mass was achieved without structured exercise in the protocol

LDL Cholesterol and Cardiovascular Risk Markers

• LDL cholesterol dropped by approximately 25%, a magnitude comparable to the effect of some lipid-lowering medications, achieved through dietary change alone over 8 weeks
• Triglycerides fell by about 32%, a reduction that would substantially lower cardiovascular risk according to established clinical thresholds
• HDL (the protective cholesterol) was not significantly changed, though there was a trend toward modest increase
• Blood pressure showed meaningful reductions, particularly systolic pressure, in a group that was not hypertensive at baseline but was at elevated risk given obesity

Metabolic Markers

• Fat oxidation increased significantly on fast days, confirming the metabolic shift to fat burning
• Resting metabolic rate was preserved throughout the 8 weeks, contradicting the concern that fasting slows metabolism
• Hunger ratings were elevated on fast days in the first two weeks but declined significantly by weeks 3 and 4, with participants reporting adaptation to the protocol

What Did Not Change

• Fat-free mass (lean tissue and muscle) — preserved throughout
• Resting metabolic rate — maintained without the metabolic slowdown seen in continuous calorie restriction
• Dietary quality on feast days — participants did not overcompensate on ad libitum days to the degree that would nullify the fast-day deficit

What the Researchers Concluded

The authors concluded that alternate day modified fasting is an effective dietary strategy for producing weight loss and improving cardiovascular risk markers, particularly LDL cholesterol and triglycerides, over an 8-week period in obese adults. They noted that the preservation of lean mass and resting metabolic rate distinguished ADMF from traditional continuous calorie restriction, which commonly produces reductions in both.

What This Means If You Fast

• LDL reductions of this magnitude are clinically meaningful. A 25% reduction in LDL is comparable to what many patients see from dietary interventions recommended by cardiologists, and was achieved through a straightforward eating pattern rather than a medically supervised elimination diet.
• Triglyceride reduction is one of the clearest benefits of fasting. The 32% drop seen here is consistent with what other fasting studies report, and triglycerides are increasingly recognised as an important independent cardiovascular risk factor.
• Muscle preservation during fasting is real, not just theoretical. The finding that fat-free mass was maintained while fat mass fell nearly 17% supports the claim that fasting does not burn muscle when practised correctly, provided protein intake is adequate during eating windows.
• The metabolic rate finding matters. One of the most common fears about fasting is that it will slow metabolism. This study found resting metabolic rate was maintained over 8 weeks — consistent with what the broader literature shows for intermittent fasting protocols compared to continuous caloric restriction.
• Hunger reduces over time. Participants who found fast days difficult in weeks 1 and 2 reported meaningful adaptation by weeks 3 and 4. This mirrors what most people experience: fasting becomes easier, not harder, with practice.
• Individual results vary. This was a small pilot study (n=16) and the findings, while consistent with other research, need replication in larger and more diverse populations.

Study Limitations

• Very small sample size (n=16): Results from 16 participants, while internally consistent, cannot be generalised to broader populations with confidence. The study was designed as a pilot to test feasibility and generate effect-size estimates for larger trials.
• No active control group: All 16 participants were in the ADMF arm. Without a parallel group on a different diet, it is difficult to attribute all changes directly to the fasting pattern versus the overall caloric deficit.
• Short duration (8 weeks): Cardiovascular risk marker changes over 8 weeks do not predict what happens over years of sustained fasting. Long-term sustainability and maintenance of improvements are separate questions.
• Participants were provided fast-day meals: In real-world practice, people choose their own foods. The provided meals ensured nutritional consistency but may not reflect typical fasting outcomes.
• Predominantly obese adults at baseline: The degree of improvement seen in people with obesity may be larger than what someone already at a healthy weight would experience.
• No measurement of direct vascular function markers: Flow-mediated dilation (FMD) or pulse wave velocity (PWV) were not assessed. Blood pressure and lipid improvements suggest reduced vascular risk, but direct endothelial function assessment was outside the scope of this pilot.

Source

Varady KA, Bhutani S, Church EC, Klempel MC. Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr. 2009;90(5):1138–1143. PMID: 19793855

Frequently Asked Questions

How much can intermittent fasting lower LDL cholesterol?

This study found a 25% reduction in LDL over 8 weeks of alternate day fasting. Other studies have reported LDL reductions of 15–30% with various fasting protocols. Results vary based on baseline LDL, diet quality during eating windows, and individual metabolic response. Anyone on cholesterol-lowering medication should consult their doctor before starting.

Does intermittent fasting lower triglycerides?

Yes, triglyceride reduction is one of the most consistent findings across fasting research. This study found a 32% drop in 8 weeks. Intermittent fasting reduces triglycerides primarily by lowering fasting insulin and reducing the liver's production of VLDL particles, which carry triglycerides into the bloodstream.

Does alternate day fasting cause muscle loss?

This study found lean mass was preserved throughout 8 weeks of ADMF even as fat mass fell by nearly 17%. This is consistent with other research showing muscle is not preferentially burned during intermittent fasting, provided protein intake is adequate during eating windows.

Does intermittent fasting slow metabolism?

This study found resting metabolic rate was maintained over 8 weeks, in contrast to what is typically seen with continuous calorie restriction which can lower RMR over time. This is one of the proposed advantages of intermittent fasting patterns over traditional dieting.

Is alternate day fasting suitable for someone wanting to improve heart health?

The cardiovascular risk marker improvements seen in this study (LDL -25%, TG -32%, blood pressure reduction) are clinically meaningful. However, anyone with a diagnosed cardiovascular condition, or taking medication for blood pressure or cholesterol, should discuss any dietary changes with their cardiologist before starting.

Related Research and Articles

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• Can intermittent fasting lower blood pressure?
• Intermittent fasting and metabolism: what science says
• What is alternate day fasting and does it work?

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