Alternate-Day Fasting vs. Daily Calorie Restriction for Weight Loss and Cardiovascular Health: 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

Alternate-day fasting (ADF) — alternating between very low-calorie days and unrestricted eating days — is one of the oldest and most studied forms of intermittent fasting. But until 2017, no rigorous long-term trial had directly compared it against the clinical standard for weight loss: daily calorie restriction.

This study asked a straightforward question: does ADF produce better weight loss and cardiovascular protection than simply eating 25% fewer calories every day? Researchers at the University of Illinois at Chicago enrolled 100 metabolically healthy adults with overweight or obesity and followed them for a full year.

For context on what ADF and cardiovascular risk reduction have in common, see our overviews of intermittent fasting and weight loss research and intermittent fasting and inflammation.

Who Was Studied

Participant profile: Adults aged 18–65, BMI 25–49.9 kg/m², metabolically healthy (no type 2 diabetes, no diagnosed cardiovascular disease, no blood pressure medication). Approximately 86% female.

How ADF worked in this study: On fast days, participants consumed 25% of their estimated energy needs — roughly 500 calories — in a single lunch meal provided by the research team. On feast days (every other day), they could eat freely with no calorie guidance. The pattern alternated continuously throughout the 6-month intervention.

How CRR worked: Participants ate 75% of their estimated energy needs every single day — a standard moderate calorie restriction of approximately 25% below maintenance. No specific meal timing restrictions.

What the Researchers Found

Body Weight

• Both ADF and CRR produced significant weight loss compared to the control group — a meaningful finding in itself.
• ADF was not significantly better than CRR for total weight loss at either 6 or 12 months. The modest numeric advantage at 6 months was not statistically significant.
• During the 6-month maintenance phase, both ADF and CRR participants maintained their losses without further structured intervention.

Cardiovascular Risk Markers

This is where the study produced its most discussed finding.

• The LDL finding was the study's headline concern. ADF participants had meaningfully higher LDL cholesterol compared to CRR participants at 6 months. The researchers noted this as an unexpected finding warranting further investigation.
• Blood pressure improvements were similar in both groups — roughly 3–4 mmHg systolic reductions — compared to the control group, but ADF held no advantage over daily restriction.
• Inflammatory markers and fasting insulin improved in both groups versus control.

Body Composition

• Fat mass: Both ADF and CRR reduced fat mass compared to control. No significant difference between ADF and CRR.
• Fat-free mass (muscle): Both groups maintained lean mass similarly — an important finding. ADF did not cause greater muscle loss than daily restriction.

What Did Not Change

• Fasting glucose did not improve significantly in either intervention group compared to control — likely because participants were already metabolically healthy at baseline.
• Lean body mass was preserved equally in both groups.
• Adherence: ADF participants found fast days harder than feast days, and overall adherence to the protocol was lower in ADF than CRR by the end of 12 months.

What the Researchers Concluded

Alternate-day fasting was not superior to daily calorie restriction for weight loss or cardiometabolic risk reduction in metabolically healthy obese adults. Both approaches worked. The unexpected elevation in LDL cholesterol in the ADF group raised caution about its cardiac safety compared to standard restriction, and the researchers concluded that ADF did not offer a clinical advantage that would justify its additional complexity.

What This Means If You Fast

• ADF works for weight loss — if you can adhere to it. Losing approximately 6% of body weight over 6 months is clinically meaningful. The question is whether the feast-fast-feast pattern is sustainable for you personally.
• Daily 25% calorie reduction achieves the same result — and appeared to be easier to maintain over 12 months. If you're choosing between ADF and a simple daily eating window, the evidence doesn't favour ADF on outcomes.
• The LDL finding deserves honest attention. Higher LDL in the ADF group at 6 months doesn't necessarily mean cardiac harm — LDL particle size (which this study didn't measure) matters significantly. But it's a signal worth monitoring if you practice strict ADF long-term.
• Most people reading this aren't doing strict ADF. This study used a very specific ADF protocol — 500 calories every other day, alternating. Many people doing "alternate day fasting" in practice eat more than 500 calories on fast days or mix it with other protocols. The findings may not apply directly to less strict versions.
• Short eating windows (16:8, 18:6) were not studied here. The time-restricted eating research shows a somewhat different metabolic picture than ADF. This study is specifically about calorie-alternating ADF, not time restriction.

Study Limitations

• Predominantly female sample (~86%): results may not generalize equally to men.
• Metabolically healthy participants: People with diabetes, hypertension, or metabolic syndrome may respond differently — this group had less room for metabolic improvement at baseline.
• Self-reported dietary intake on feast days and outside of supervised meals introduces potential inaccuracy.
• Single-site study at one US institution with a homogeneous participant pool.
• ADF adherence declined over time, which may have narrowed the apparent difference between groups.
• LDL particle size was not measured, leaving the cardiovascular significance of the LDL finding uncertain.
• 12 months is not long-term. Whether any differences emerge over years of practice is unknown.

Source

Trepanowski JF, Kroeger CM, Barnosky A, Klempel MC, Bhutani S, Hoddy KK, Gabel K, Freels S, Rigdon J, Rood J, Ravussin E, Varady KA. (2017). Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults. JAMA Internal Medicine, 177(7), 930–938. PMID: 28459931

Frequently Asked Questions

Is alternate-day fasting better than regular calorie restriction for weight loss?

Based on this RCT, no. Over 6 and 12 months, both approaches produced similar weight loss of around 5–6% of body weight. ADF did not show a significant advantage over daily 25% calorie restriction.

Why did ADF raise LDL cholesterol in this study?

The researchers noted this as an unexpected finding and could not definitively explain it. One hypothesis is that ADF's alternating pattern creates larger fluctuations in free fatty acid release, which may influence LDL production. Another is that LDL particle size (not measured) may have shifted toward larger, less harmful particles — common during ketogenic-like states.

Does intermittent fasting raise or lower cholesterol?

It depends on the type and context. Most studies on time-restricted eating (16:8 or similar) show modest improvements in triglycerides and neutral or slightly positive effects on LDL. The ADF-specific LDL finding in this study may not apply to shorter eating window approaches.

How many calories do you eat on ADF fast days?

In this study, fast days were 500 calories — 25% of average estimated energy needs. Many real-world ADF protocols allow up to 600–800 calories. The strict 500-calorie approach used here is challenging to maintain long term.

Is alternate-day fasting safe for cardiovascular health?

This study raised questions rather than answering them definitively. Blood pressure and triglycerides improved similarly to daily restriction, but the LDL elevation warrants monitoring. Anyone with known cardiovascular disease or high cholesterol should discuss ADF with their doctor before starting.

Related Research and Articles

• Intermittent fasting and weight loss: what 50 studies show
• Does intermittent fasting help with high cholesterol?
• What is alternate day fasting and does it work?
• Intermittent fasting and metabolism: what science says
• Intermittent fasting benefits: the complete science-backed guide

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