Can Keto Help with PCOS?
It may, for some women. The reasoning centers on insulin. Insulin resistance is common in PCOS, including in women who are not overweight, and high insulin encourages the ovaries to produce more androgens such as testosterone. Those androgens are behind many PCOS symptoms. Cutting carbohydrate to around 20 to 25 g of net carbs a day lowers the insulin response to meals, which may ease that pressure.
The clinical evidence is still early. A 2005 pilot study in Nutrition & Metabolism put 11 women with PCOS on a ketogenic diet for 24 weeks. The five who finished lost about 12% of their body weight on average and had lower fasting insulin, lower free testosterone, and a lower LH/FSH ratio. Two became pregnant despite previous fertility problems. That is a small, uncontrolled study, so it supports trying the approach with your doctor's input rather than proving it works. Larger trials are needed.
How Keto May Affect PCOS Symptoms
Insulin and blood glucose
Cutting carbohydrate reliably lowers the glucose and insulin rise after meals, and fasting insulin often falls as well. This is the best-supported part of the picture, and it can show up on blood tests within weeks. Your doctor can track fasting glucose, insulin, or HbA1c to see whether it is happening for you.
Testosterone and androgen levels
Insulin stimulates the ovaries to make androgens, so lowering insulin may lower androgens too. The 2005 pilot study saw free testosterone fall over 24 weeks. Whether the same happens for you depends on how much insulin is driving your PCOS, and only a blood test can tell.
Menstrual regularity
Some women report more regular cycles on keto, and weight loss on any diet can help ovulation return in women with PCOS who are overweight. The keto-specific evidence is limited to small studies. If your periods are absent or very irregular, or you are trying to conceive, keep your OB-GYN involved.
Calculating Keto Macros for PCOS
The calculation follows standard keto: estimate your daily calorie burn, apply your goal, then split the calories. The PCOS-specific part is net carbs. If you select insulin resistance, the target is 20 g a day; if you select no or unsure, it is 25 g. Both are at the strict end of the 20 to 50 g range, which keeps the insulin-lowering effect front and center.
Protein uses the same rule as for everyone: about 0.8 g per pound of lean body mass (1.76 g per kg), with lean mass taken from your body fat percentage or estimated with the Boer formula. Fat fills the rest. A moderate deficit, around 500 kcal a day, is usually easier to sustain than a large one, and calories never go below 1,200 a day.
What to Eat on Keto with PCOS
Build meals on whole foods: fatty fish such as salmon, sardines, and mackerel; eggs; meat and poultry; leafy greens and other non-starchy vegetables within your carb budget; avocado and olive oil. These make it easier to hit protein while keeping net carbs low, and they supply magnesium, folate, and omega-3 fats.
Some foods are worth watching. Milk and whey can raise insulin more than their carb content suggests, so some women prefer cheese, cream, and butter to glasses of milk or protein shakes. Highly processed "keto" snacks and large amounts of nuts make it easy to overshoot calories without feeling full.
Keto and PCOS Medications
Talk to your prescribing doctor before you start
Metformin: Commonly prescribed for insulin resistance in PCOS and often combined with a lower-carb diet. On its own, metformin rarely causes low blood sugar; the risk rises when it is taken with other glucose-lowering drugs (such as insulin or sulfonylureas), with heavy alcohol, or with very low food intake. Stomach upset is the most common side effect, and long-term use can lower vitamin B12. Do not change your dose without your prescribing doctor.
Hormonal contraceptives: If you use the pill partly to manage PCOS symptoms, tell your OB-GYN you are changing your diet, so changes in weight, cycles, or symptoms can be read in context.
Fertility medications (Clomid, Letrozole, gonadotropins): If you are undergoing fertility treatment, coordinate any diet change with your reproductive endocrinologist.
SGLT2 inhibitors and insulin: If you take these for diabetes, a ketogenic diet needs medical supervision. SGLT2 inhibitors carry a warning about ketoacidosis, which a very low-carb diet can make more likely.
Realistic Expectations
Women with PCOS and insulin resistance often lose weight more slowly than they expect. That is not a failure of the diet or of willpower. After the first week or two, when some quick water loss is normal, around 0.5 to 1 pound a week is a realistic pace for many women. Blood markers such as glucose, insulin, and triglycerides often improve before the scale moves much, and those changes matter in their own right.
Hormone changes, where they happen, take months rather than weeks, and they vary a lot from person to person. Keto is one dietary option for PCOS, not a cure, and it works best as part of a plan you have agreed with your doctor. Steady habits over several months matter more than a perfect week.