How should I read a page where the grades disagree?

Start with the strong-evidence entries, because those are the findings most likely to still be true in five years. Then read the contested ones to understand what the honest objections are — not to dismiss them. The order matters. Reading the contested material first tends to produce false confidence in whichever side you already preferred; reading it after the replicated work gives you a baseline to measure it against.

Does this site take a position on sleep & circadian?

Where the literature is clear, yes — and the papers behind that position are on this page. Where it genuinely is not clear, the page says so rather than manufacturing certainty. The commitment is narrower than it sounds: we will not describe a contested question as settled to make a protocol sound more impressive, and we will not bury a trial because it complicates the story.

Why are some of these papers decades old?

This topic spans 2004 to 2017 across 8 journals. Age is not a defect in physiology research — a well-run metabolic-ward study from the 1990s can be more informative than a large observational survey published last year. What matters is the design and whether the finding has held up. Where an older paper has been superseded or failed replication, its grade is lowered rather than the entry being silently deleted.

What should I actually do with this?

Use it to ask better questions. A citation library describes what happened to groups of people in trials; it cannot tell you what is happening inside your body, what interacts with your medication, or what your bloodwork means. The practical route is to read the papers that apply to your situation, then take the specific questions they raise to a clinician who can examine you and look at your labs.

Sleep & Circadian · 9 cited studies

Research on Sleep & Circadian Rhythm

Q: How solid is the evidence on sleep & circadian?

Of the 9 papers filed under this topic, 5 carry a strong-evidence grade — replicated trials or large meta-analyses — and 0 sit in the contested or mechanism-only tiers where the human outcome has not been settled. A mixed distribution is normal and honest. Topics where every paper is graded strong are usually topics where the inconvenient papers have been quietly left out.

Sleep restriction, circadian misalignment, and metabolic health — Spiegel, Buxton, Scheer, Cappuccio, the AHA scientific statement.

See the studies All research

Papers

Strong evidence

04–17

Years covered

01The state of the evidence

Where this literature sits

Sleep is not optional metabolic infrastructure. Spiegel's 2004 leptin/ghrelin paper showed that two nights of 4-hour sleep dropped leptin 18%, raised ghrelin 28%, and increased subjective hunger 24% — appetite hormones flip in days. Buxton 2012 (Science Translational Medicine) demonstrated that 3 weeks of sleep restriction combined with circadian disruption produced prediabetic-grade insulin resistance and lower resting metabolic rate.

Scheer's 2009 PNAS forced-circadian-misalignment study produced inverted cortisol rhythms and postprandial hyperglycemia in 10 days. The AHA's 2016 scientific statement (St-Onge) summarises the cardiometabolic consequences. Stothard 2017 showed camping for a week realigned circadian phase by ~2 hours.

Below: the foundational sleep/circadian literature.

Evidence mix on this topic

Strong evidence5
Moderate evidence4

Years covered2004–2017

Journals8

Paywalled summaries0

02The studies

Every paper behind the claim

Filter by grade or flip the order. Each card links straight to PubMed, the DOI or the journal — read the original rather than our summary of it.

Moderate evidence2017
Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend
Stothard ER et al. · Current Biology
Camping for 6 days realigned circadian phase by ~2 hours; modern indoor lighting delays sleep onset.
Sleep & CircadianSource ↗
Strong evidence2016
Sleep Duration and Quality: Impact on Lifestyle Behaviors and Cardiometabolic Health (AHA scientific statement)
St-Onge MP et al. · Circulation
AHA position: short sleep (<7 h) consistently associated with weight gain and worse cardiometabolic risk.
Sleep & CircadianSource ↗
Moderate evidence2015
Natural sleep and its seasonal variations in three pre-industrial societies
Yetish G et al. · Current Biology
Hadza, San and Tsimane sleep ~6.5 h/night — fewer hours than Westerners but better consolidation.
Sleep & CircadianAncestral DietSource ↗
Moderate evidence2013
Timing of food intake predicts weight loss effectiveness
Garaulet M et al. · International Journal of Obesity
Late lunch eaters lost ~25% less weight on identical-calorie programs than early eaters over 20 weeks.
Sleep & CircadianSource ↗
Strong evidence2012
Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption
Buxton OM et al. · Science Translational Medicine
3 weeks of sleep restriction + circadian disruption produced prediabetic-grade insulin resistance and lower metabolic rate.
Sleep & CircadianInsulin ResistanceSource ↗
Strong evidence2009
Adverse metabolic and cardiovascular consequences of circadian misalignment
Scheer FAJL et al. · Proceedings of the National Academy of Sciences
Forced 12-hour circadian misalignment for 10 days produced postprandial hyperglycemia and inverted cortisol rhythm.
Sleep & CircadianSource ↗
Strong evidence2008
Meta-analysis of short sleep duration and obesity in children and adults
Cappuccio FP et al. · Sleep
Meta-analysis: short sleep (<5 h) was associated with 55% higher obesity risk in adults across 30 studies.
Sleep & CircadianSource ↗
Moderate evidence2007
The metabolic consequences of sleep deprivation
Knutson KL et al. · Sleep Medicine Reviews
Review of cross-sectional and lab evidence linking sleep loss to obesity, T2D risk, appetite dysregulation.
Sleep & CircadianSource ↗
Strong evidence2004
Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite
Spiegel K et al. · Annals of Internal Medicine
Two nights of 4-hour sleep dropped leptin 18%, raised ghrelin 28%, increased hunger ratings 24% — appetite hormones flip in days.
Sleep & CircadianSource ↗

03Related research

Nothing metabolic sits on its own

Sleep moves insulin. Stress moves visceral fat. Protein moves total intake. The other shelves in the library are usually where the missing half of the answer lives.

The full library Essays on this

04Straight answers

Sleep & Circadian

Reading this evidence honestly

Of the 9 papers filed under this topic, 5 carry a strong-evidence grade — replicated trials or large meta-analyses — and 0 sit in the contested or mechanism-only tiers where the human outcome has not been settled.

A mixed distribution is normal and honest. Topics where every paper is graded strong are usually topics where the inconvenient papers have been quietly left out.

Strong evidence56%

5 of 9 papers

Moderate evidence44%

4 of 9 papers

Evidence grades describe the strength of the research, not a promise about your outcome.

Papers describe populations. Your labs describe you.

The free assessment takes the research above and asks which parts of it apply to your pattern — then names the protocol the evidence actually supports for it.

Take the free assessment Free calculators

Every claim citedOpen the paper, check us.

Graded honestlyContested is labelled contested.

No guaranteed numbersIndividual results vary.

Educational only, not medical advice. Citing a study is not a recommendation to act on it. Consult your physician before major dietary changes or altering prescribed medication. These statements have not been evaluated by the Food and Drug Administration. Individual results vary; no outcome is guaranteed.

Research on Sleep & Circadian Rhythm

Where this literature sits

Every paper behind the claim

Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend

Sleep Duration and Quality: Impact on Lifestyle Behaviors and Cardiometabolic Health (AHA scientific statement)

Natural sleep and its seasonal variations in three pre-industrial societies

Timing of food intake predicts weight loss effectiveness

Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption

Adverse metabolic and cardiovascular consequences of circadian misalignment

Meta-analysis of short sleep duration and obesity in children and adults

The metabolic consequences of sleep deprivation

Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite

Nothing metabolic sits on its own

Reading this evidence honestly

Papers describe populations. Your labs describe you.