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Hormones during weeks of fasting

Glucagon levels and metabolic effects in fasting man.

Overview

Marliss EB et al.. J Clin Invest 1970 · PMID 5480852 · DOI 10.1172/JCI106445

During fasts of up to six weeks, insulin fell to a low plateau by the third day and stayed there; glucagon rose.

Does the study support the specific claim? Partly · Methodological quality: moderate

Study explained simply

What did the researchers want to find out?: Describe glucagon and insulin in prolonged human fasting.
How was the study done?: Repeated blood measurements during supervised fasts; glucagon infusions.
How many people, animals or samples were studied?: Volunteers on 6-week fasts (number not in abstract).
What was actually found?: Insulin fell to a plateau by day 3; glucagon peaked on day 3.
How large was the observed effect?: Not reported in abstract.
What do the results mean in everyday life?: Fasting lowers insulin, but a low basal level remains.
What are the study's limitations?: Old, small, uncontrolled; abstract only.
What does it say about Elawady's specific claim?: Correct that insulin falls; wrong that it becomes zero.
Do the results apply to Germany and Europe?: Applies; same physiology.
What can explicitly not be concluded from this study?: Exact insulin concentrations; effects in lean people.

Authors: Marliss EB et al.
Journal: J Clin Invest
Year: 1970
Identifier: PMID 5480852 DOI 10.1172/JCI106445
Verification: verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
Retracted: no
Corrections: none
Extent checked: abstract only
Conflicts of interest and funding: not stated in abstract

How do glucagon and insulin change during prolonged (up to 6 weeks) fasting in humans?

Study design: Other – Physiological study of hormone levels during 6-week therapeutic fasts plus glucagon infusion experiments
Population: Adults undergoing supervised prolonged fasts (obese volunteers; details not in abstract)
Country: USA (not stated in abstract)
Period: not stated in abstract
Sample size: not stated in abstract
Inclusion and exclusion criteria: not stated in abstract

Exposure / intervention: Total fasting up to 6 weeks; glucagon infusions in 4-6-week fasted subjects
Comparator: Post-absorptive state
Endpoints: Plasma glucagon, insulin, amino acids, glucose, ketone metabolism
Statistical methods: Descriptive time courses (abstract)

Results: Plasma glucagon rose twofold to a peak on day 3 of fasting, then declined to a level at or above post-absorptive; 'Insulin concentration declined to a plateau by the 3rd day.' A persisting altered glucagon/insulin relationship characterised the fasted state.
Absolute risks: not reported
Authors' conclusion: A synergism of low insulin and relatively or absolutely raised glucagon controls hepatic substrate extraction for gluconeogenesis in prolonged fasting.

Qualitative: insulin falls and then stays at a plateau; it is not reported to disappear.

Directly tests whether insulin reaches zero during fasting: insulin falls to a plateau (a persisting low level), not to zero.

Consistent with modern 72-h fasting reference data (I-FAST-103) and 36-h fasting studies (I-FAST-102).

Universal biology; applies in Europe and Egypt.

Supports the correct kernel (insulin falls) and contradicts 'insulin equals zero'.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	moderate
Risk of bias	not assessable
Precision of results	not applicable
Directness	direct
Reproducibility	replicated
Consistency with the overall evidence	consistent
Regional transferability	high
Adequacy of the interpretation (by the archive)	not applicable