Does creatine spike insulin?

Not on its own, in the trials that measured it. Green 1996 found 5 g of creatine in water had no effect on serum insulin, while the same dose followed by 93 g of sugar raised insulin sharply. Rooney 2003 found no difference in the insulin response to a glucose drink after 42 days of 5 g a day in vegetarians. What raises insulin is the carbohydrate or protein taken with it.

Does creatine break ketosis?

No study has measured ketone levels after creatine. Creatine itself is not a carbohydrate and is not converted to glucose for energy; about 1–2% of the body's muscle creatine is lost as creatinine each day rather than burned. The ketosis risk comes from what a product adds: a chew with 4.5 g of sugar is a small carbohydrate dose, and label totals are the only numbers available.

Does creatine mess up autophagy?

This has not been studied in humans. PubMed's three records combining creatine supplementation and autophagy are mouse studies of obesity, cancer wasting and a neurological disease, and none looked at fasting. Any confident answer either way is not based on a human measurement.

Does creatine break a fast for blood work?

The fasting rule before a blood test is about glucose and lipids, and plain creatine has no calories to disturb them. Creatine does raise blood creatinine, the kidney marker, independently of fasting, and that is the reason to tell whoever orders the test. The mechanism is on this site's creatine-in-bloodwork page.

Is creatine allowed during Ramadan fasting?

That is a religious question this page cannot answer. On the science side, no published trial has given creatine to people fasting for Ramadan. The Ramadan studies that mention creatine measure creatine kinase or creatinine in the blood of fasting athletes; none tested a supplement.

Does Creatine Break a Fast? What Was Measured

Q: Does creatine break a fast?

It depends on which definition of breaking a fast is meant. By calories, plain creatine monohydrate is not an energy source, and 39 of 40 plain powder labels checked list no calories. By insulin, the one trial that measured creatine on its own found no effect on serum insulin. By autophagy, nobody has measured it in people. Flavoured powders, chews and gummies are a different question, because they carry sugar and calories.

Plain creatine carries no usable calories and, in the 1996 biopsy trial, left insulin where it was. What no study has done is give creatine to people who are fasting, or measure autophagy.

"Does creatine break a fast?" gets answered with confidence across page one of Google, almost always by companies that sell creatine, and almost never with a citation. The honest answer is partly measured and partly unknown. The insulin question has a trial. The calorie question has labels. The two questions intermittent fasters care about most, what happens during an actual fast and what happens to autophagy, have never been tested in people. This page reports what each source measured; it gives no advice on how to use creatine or how to fast, per our editorial standards.

What "breaking a fast" can mean

People mean at least three different things, and each has a different amount of evidence:

Definition	What would count as breaking it	Evidence for creatine
Calories	Any usable energy	Strong: creatine is not burned for energy; plain labels list none
Insulin / glucose	A rise in insulin or blood sugar	One direct trial (Green 1996) plus longer-term glucose studies
Autophagy	Switching off the cell's clean-up process	None in humans

Calories: creatine is not fuel

Creatine stores and moves phosphate inside muscle. It is not oxidised for energy the way glucose, fat or amino acids are. According to the International Society of Sports Nutrition's 2017 position stand, about 1–2% of muscle creatine is converted to creatinine each day and excreted in urine (Kreider 2017, PMC5469049). The body clears it as a waste product and never burns it.

The labels agree. Of 40 on-market, single-ingredient, unflavoured creatine monohydrate powders in the NIH Dietary Supplement Label Database (checked 2026-09-30), 39 carry no calorie row at all. The fortieth lists one, and a supplement label can leave calories out when the amount is insignificant.

Insulin: the 1996 trial measured it directly

The reason people ask about insulin is a pair of Nottingham studies that became famous for the opposite finding: that sugar taken with creatine pushes more of it into muscle.

In the biopsy trial, 24 men took 5 g of creatine in solution four times a day for five days. One group took it alone; the other took it followed 30 minutes later by 93 g of simple sugar. The sugar group stored 60% more total creatine in muscle. The finding that matters for fasting sits in the same abstract: "Creatine supplementation had no effect on serum insulin concentration," while creatine plus sugar "dramatically elevated" it (Green 1996, PMID 8944667). A companion study in 22 men found the same split (Green 1996, PMID 8899067).

Later work filled in the picture:

Study	Who, how long	What it found about insulin
Steenge 2000 (PMID 10956365)	12 men, 5 g creatine with 5 g, 50 g or 96 g carbohydrate, or 50 g protein + 47 g carbohydrate	The insulin rise came from the carbohydrate and protein; the 5 g-carbohydrate arm had the smallest response
Steenge 1998 (PMID 9843739)	7 men, insulin infused under clamp	Insulin helps muscle take up creatine only at high levels, the kind a large meal produces
Rooney 2003 (PMID 12624482)	Vegetarians, 5 g a day for 42 days vs maltodextrin	No difference in insulin response to a glucose drink; a trend (p = 0.07) to higher fasting glucose, and a larger glucose response
Gualano 2008 (PMID 17396216)	22 sedentary men, about 10 g a day for 3 months with aerobic training	Better glucose tolerance; fasting insulin and HOMA unchanged
Delpino 2022 meta-analysis (PMID 35063192)	9 studies	No significant effect on fasting glucose or insulin resistance

So the measured answer on insulin is consistent: creatine taken by itself did not raise insulin in the trial that tested exactly that. Two small studies disagree about longer-term glucose handling in opposite directions (Rooney's worse response in vegetarians, Gualano's better tolerance with training), and the pooled analysis finds no effect. None of these studies was about fasting.

What nobody has studied: creatine during a fast

The page-one answers assume a literature that does not exist. A PubMed search on 2026-09-30 combining creatine supplementation with Ramadan, fasting, time-restricted eating or intermittent fasting returned 27 records. Read one by one, none gives creatine to people during a fasting period. "Fasting" appears because blood was drawn after an overnight fast, or because fasting glucose was an outcome. A looser search for creatine with Ramadan or intermittent fasting returned 16 records, and those measure creatine kinase or serum creatinine in fasting athletes and patients. None of them tested a supplement.

The same gap applies to autophagy, which is often the whole reason for a long fast. PubMed held no human study of creatine supplementation and autophagy on 2026-09-30. The three records that combine the terms are mouse studies: of diet-induced obesity, cancer-related muscle wasting and a neurological disease. Some pages say creatine "doesn't affect autophagy" and others say it "might". Neither claim has a human measurement behind it.

Flavoured products are a label question

Once a product is flavoured or chewable, the answer is on the Supplement Facts panel. All 16 on-market creatine chew and gummy labels found in the NIH database on 2026-09-30 declare calories:

Measure (per labelled serving)	Range across the 16 labels
Calories	10 to 35
Sugars (15 of 16 declare them)	0 to 4.5 g
Chews or gummies per serving	1 to 4

One chew brand declares 30 calories and 0 g sugar, so its energy comes from something other than sugar. A serving that delivers 5 g of creatine as chews can therefore also deliver a few grams of sugar. Whether that "breaks" a fast depends on which of the three definitions above is being used. The format comparison is on creatine gummies; flavoured powders vary too, and their labels are the only source for their numbers.

Blood tests

The fasting instruction before a blood test protects glucose and lipid readings, and plain creatine has no calories to disturb those. Creatine affects a different number: it raises blood creatinine, the marker used to estimate kidney function, whether or not the person has eaten. That is the reason to mention it to whoever orders the test, and why the question belongs with creatine in bloodwork more than with fasting.

The honest summary

Calories: creatine is not burned for energy; 39 of 40 plain powder labels list none.
Insulin: creatine alone did not change serum insulin in the 1996 trial; sugar taken with it did.
During a fast: 27 PubMed records, 0 trials of creatine in fasting people.
Autophagy: 0 human studies.
Chews and gummies: 10–35 calories and up to 4.5 g sugar per serving, per their own labels.

Limits of this page

The insulin trials were small (7 to 24 men per study), mostly young men, and measured insulin over hours, not over a multi-day fast. The label counts come from what manufacturers filed with the NIH database; a label can be out of date or absent, and one brand can appear several times for different flavours. PubMed counts depend on query wording and were taken on one date. Absence of a study is reported as absence. It does not show that creatine is harmless or harmful during a fast.

Sources and dates

Green AL, Hultman E, Macdonald IA, Sewell DA, Greenhaff PL. Carbohydrate ingestion augments skeletal muscle creatine accumulation during creatine supplementation in humans. Am J Physiol 1996;271:E821–6 — PMID 8944667
Green AL, Simpson EJ, Littlewood JJ, Macdonald IA, Greenhaff PL. Carbohydrate ingestion augments creatine retention during creatine feeding in humans. Acta Physiol Scand 1996;158:195–202 — PMID 8899067
Steenge GR, Lambourne J, Casey A, Macdonald IA, Greenhaff PL. Stimulatory effect of insulin on creatine accumulation in human skeletal muscle. Am J Physiol 1998;275:E974–9 — PMID 9843739
Steenge GR, Simpson EJ, Greenhaff PL. Protein- and carbohydrate-induced augmentation of whole body creatine retention in humans. J Appl Physiol 2000;89:1165–71 — PMID 10956365
Rooney KB, et al. Creatine supplementation affects glucose homeostasis but not insulin secretion in humans. Ann Nutr Metab 2003;47:11–5 — PMID 12624482
Gualano B, et al. Effects of creatine supplementation on glucose tolerance and insulin sensitivity in sedentary healthy males undergoing aerobic training. Amino Acids 2008;34:245–50 — PMID 17396216
Delpino FM, Figueiredo LM. Does creatine supplementation improve glycemic control and insulin resistance in healthy and diabetic patients? A systematic review and meta-analysis. Clin Nutr ESPEN 2022;47:128–34 — PMID 35063192
Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. J Int Soc Sports Nutr 2017;14:18 — PMC5469049, read 2026-09-30
NIH Office of Dietary Supplements, Dietary Supplement Label Database, API queried 2026-09-30: on-market single-ingredient unflavoured creatine monohydrate powders (45 found, 40 labels read); on-market creatine chews and gummies (16 labels read).
PubMed, searched 2026-09-30: creatine supplementation or monohydrate with Ramadan / fasting / fasted / time-restricted / intermittent fasting → 27; creatine with Ramadan / intermittent fasting / time-restricted → 16; creatine supplementation or monohydrate with autophagy → 3 (all animal).

Does Creatine Break a Fast? Measured: Insulin Did Not Move, and Nobody Has Tested It During a Fast