Quick answer: Common signs of ketosis include reduced appetite, steadier energy and focus, fruity or metallic breath from acetone, more thirst and urination, and early weight loss. Signs are only clues; a blood, breath or urine ketone test confirms it. If you’re not in ketosis, check hidden carbs and protein, stay active and give it time.
Key takeaways
Common signs of ketosis include reduced appetite, steadier energy and focus and a distinctive keto breath.
Signs are only clues, so testing ketones is the way to confirm ketosis.
Fruity breath with nausea, vomiting, abdominal pain or confusion, especially in someone with diabetes, can signal ketoacidosis and needs urgent care.
Common signs
Reduced appetite
Ketones and filling fats may reduce hunger.
Steadier energy and focus
Many people notice steadier energy once adapted.
Keto breath
Acetone can give breath a fruity or metallic smell.
More thirst and urination
Early on, the body releases water and sodium.
Early weight loss
Often water at first, then fat.
Confirming ketosis
Signs are clues, not proof. See how to test ketones.
If you’re not in ketosis
Double-check your macros (see keto macro calculator), look for hidden carbs in sauces and snacks, and increase physical activity. Some people add a time-restricted eating window (see intermittent fasting). Give your body a few days to adapt.
A safety note
Fruity breath with nausea, vomiting, abdominal pain or confusion, especially in people with diabetes, can signal ketoacidosis and needs urgent care.
Healthy aging lens
Learning how your body responds to food builds metabolic awareness. See what is ketosis.
What the research shows
The signs people associate with ketosis have been recorded in studies and online reports.
What “keto flu” looks like (Bostock 2020, analysis of online reports). Researchers reviewed 448 posts from 300 people in 43 online forums. The most common complaints were flu-like feelings, headache, fatigue, nausea, dizziness, brain fog and stomach upset, mostly in the first week and fading by about 4 weeks; the few people who reported when symptoms ended said it took a median of 4.5 days. A limitation is that these were self-reports on the internet, not a clinical study, so true frequency is unknown.
Six weeks of keto in healthy adults (Urbain 2017, before-and-after study). 42 healthy adults followed a ketogenic diet (about 72% fat, 21% protein and 8% carbohydrate) without calorie limits for 6 weeks. They lost about 2 kg, split equally between fat and lean mass. Peak power dropped 4%, LDL cholesterol rose about 11%, and insulin fell 22%. A limitation is that there was no control group, so changes can’t be fully separated from other factors.
When to test ketones (Urbain 2016, monitoring study). 12 healthy adults in their sixth week of a ketogenic diet tested urine 8 times and blood 18 times over 24 hours. Blood beta-hydroxybutyrate was lowest around 10 a.m. (0.33 mmol/L) and highest around 3 a.m. (0.70 mmol/L), and urine strips detected ketosis most reliably (over 90% of the time) in early-morning and after-dinner samples. A limitation is the small group of healthy volunteers.
Strength of the evidence: Symptoms are an unreliable guide to ketosis; testing gives a clearer answer, and many early symptoms fade within a few weeks.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have diabetes or take insulin, sulfonylureas or SGLT2 inhibitors (risk of low blood sugar or ketoacidosis), or if you take blood pressure medication or diuretics. The same is true if you have kidney, liver, gallbladder or pancreas disease, or high cholesterol, if you are pregnant, breastfeeding, or have a history of disordered eating, or if you want a keto plan tailored to your labs and goals.
See a medical provider promptly for nausea and vomiting, abdominal pain, confusion, fruity-smelling breath with rapid breathing, or very high blood sugar or ketone readings, which can signal ketoacidosis.
Want a keto plan that’s safe for your health?
A free 15-minute consultation with Dr. Kneessi. No cost, no obligation. In-office in Odenton, MD or by telehealth.
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Which way of testing ketones would you suggest for me?
Which signs of ketosis should I look for in my own body?
Are there signs that would tell me something is not right?
Would testing my ketones be more reliable than going by symptoms?
Frequently asked questions
What are the signs of ketosis?
Less hunger, steadier energy, keto breath, thirst and early weight loss.
What is keto breath?
A fruity or metallic smell from acetone.
How do I know for sure?
Test blood, breath or urine ketones.
Why am I not in ketosis?
Hidden carbs, too much protein or not enough time are common reasons.
Sources
- Anderson JC. Measuring breath acetone for monitoring fat loss: Review. Obesity (Silver Spring) 2015. PMID: 26524104. https://pmc.ncbi.nlm.nih.gov/articles/PMC4737348/
- Gibson AA, et al. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obes Rev 2015. PMID: 25402637. https://pubmed.ncbi.nlm.nih.gov/25402637/
- Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr 1992. PMID: 1615908. https://pubmed.ncbi.nlm.nih.gov/1615908/
- Dhatariya KK, et al. Diabetic ketoacidosis. Nat Rev Dis Primers 2020. PMID: 32409703. https://pubmed.ncbi.nlm.nih.gov/32409703/
- MedlinePlus: Ketones in Blood
- MedlinePlus: Diabetic Ketoacidosis
- Bostock ECS, et al. Consumer Reports of “Keto Flu” Associated With the Ketogenic Diet. Front Nutr 2020. PMID: 32232045. https://pubmed.ncbi.nlm.nih.gov/32232045/
- Urbain P, et al. Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults. Nutr Metab (Lond) 2017. PMID: 28239404. https://pubmed.ncbi.nlm.nih.gov/28239404/
- Urbain P, Bertz H. Monitoring for compliance with a ketogenic diet: what is the best time of day to test for urinary ketosis? Nutr Metab (Lond) 2016. PMID: 27822291. https://pubmed.ncbi.nlm.nih.gov/27822291/
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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