Keto and Perimenopause: An Honest Look at What Works and What Backfires

Why Women in Perimenopause Are Drawn to Keto

Stubborn belly fat. Blood sugar swings. Energy crashes after meals. These are real experiences in perimenopause, and keto promises to address all of them.

The appeal makes sense. Ketogenic eating eliminates refined carbohydrates, reduces insulin spikes, and shifts the body toward fat burning. For some women, this combination produces noticeable improvements in how they feel and how their body composition changes.

But perimenopause introduces a layer of complexity that makes keto a more nuanced choice than it is for someone in their thirties. Understanding that complexity helps you decide whether it's worth trying, and how to approach it if you do.

What Keto Actually Is

A true ketogenic diet is very high in fat (typically 70-75% of calories), very low in carbohydrates (usually under 20-50 grams per day), and moderate in protein. The goal is to push the body into ketosis, a metabolic state where fat is broken down into ketone bodies that serve as the primary fuel source instead of glucose.

This is a significant metabolic shift. It takes one to three weeks to fully adapt, a period sometimes called the keto flu, during which fatigue, headaches, and irritability are common.

Keto is different from simply eating low-carb or reducing sugar. Low-carb eating (100-150 grams of carbohydrates per day) doesn't necessarily produce ketosis but still reduces insulin response and improves blood sugar regulation. This distinction matters when thinking about perimenopause.

Where Keto Can Actually Help

The strongest case for keto in perimenopause is insulin resistance. As estrogen declines, insulin sensitivity often decreases, particularly around the abdomen. If your fasting insulin is elevated or you've been told you're prediabetic, a ketogenic approach can produce meaningful improvements in insulin sensitivity and fasting glucose.

Some women also report clearer mental focus once they're adapted to ketosis. The brain can run efficiently on ketones, and some research suggests ketones may be neuroprotective. Women with a family history of Alzheimer's sometimes find this aspect of keto compelling.

For weight management, particularly visceral fat reduction, keto can be effective, especially in the first several months. Reducing insulin lowers the body's tendency to store fat, and many women experience reduced appetite on a high-fat diet.

If you have epilepsy, PCOS, or type 2 diabetes, there's substantial research supporting ketogenic approaches. Talk to your doctor about whether it's appropriate for your situation.

The Cortisol Risk Most People Don't Mention

Here's the part that often gets left out of keto enthusiasm. Severe carbohydrate restriction raises cortisol.

When your body is in ketosis, it treats low carbohydrate availability as a mild stress signal. In response, cortisol rises to ensure your liver produces enough glucose for the tissues that still require it (the brain, red blood cells, adrenals). This is a normal physiological response.

In perimenopause, cortisol is already under pressure. Sleep disruption raises cortisol. The HPA axis (the hormonal stress-response system) becomes more reactive as sex hormones shift. Many women are already running on elevated baseline cortisol from life demands on top of sleep loss.

Adding the cortisol stimulus of strict keto to an already stressed system can backfire. Elevated cortisol promotes abdominal fat storage, disrupts sleep further, worsens mood, and can suppress thyroid function. Some women find that strict keto actually worsens the belly fat and fatigue they were trying to address.

This doesn't mean keto is wrong for everyone in perimenopause. But it means that chronic, strict ketosis in a high-stress context can work against your goals.

How Keto Can Affect Your Hormones and Thyroid

Very low carbohydrate intake can reduce the conversion of T4 (inactive thyroid hormone) to T3 (active thyroid hormone). Thyroid function already tends to become less robust during perimenopause, and subclinical hypothyroidism is more common in this age group.

If your thyroid function is already borderline, the additional downward pressure from strict keto can tip you into more pronounced symptoms: fatigue, cold sensitivity, brain fog, and weight gain.

Sex hormone binding globulin (SHBG) is another consideration. Insulin lowers SHBG, and SHBG binds to estrogen and testosterone, regulating how much free hormone circulates. A diet that dramatically lowers insulin will raise SHBG, potentially lowering free estrogen at a time when estrogen is already declining. For some women, this is irrelevant. For others, it can intensify symptoms.

These are not reasons to dismiss keto entirely, but they're reasons to monitor how you feel and get appropriate labs if you're making a significant dietary shift.

Cyclical Keto: A More Perimenopause-Friendly Approach

One approach that addresses both the benefits and the risks is cyclical ketogenic eating. Rather than maintaining strict ketosis every day, you cycle through periods of lower and higher carbohydrate intake.

A common pattern is five days of ketogenic eating followed by one or two higher-carbohydrate days. The higher-carb days, sometimes called carb refeeds, serve several purposes. They replenish glycogen stores, reduce the cortisol stimulus of prolonged restriction, support thyroid hormone conversion, and can make the overall pattern more sustainable.

Carb refeeds don't need to involve sugar or processed food. They might mean adding sweet potato, fruit, legumes, or whole grains back in for a day. The goal is bringing carbohydrates to around 100-150 grams, not unlimited eating.

This approach captures many of keto's metabolic benefits while reducing the chronic stress load. For women who are also exercising regularly, it also better supports workout performance and recovery.

Low-Carb Without Full Ketosis: Often the Smarter Middle Ground

For many women in perimenopause, the sweet spot isn't true ketosis. It's reducing carbohydrates meaningfully without going so low that you trigger chronic cortisol elevation.

Eating 75-100 grams of carbohydrates per day from whole food sources (vegetables, legumes, some fruit, minimal grains) reduces insulin response, supports weight management, and improves blood sugar stability. It doesn't put the body into ketosis, so the cortisol and thyroid effects are less pronounced.

This range also leaves room for the fiber-rich foods that support the gut microbiome and the phytonutrients that reduce inflammation. Strict keto is necessarily low in legumes, fruits, and many vegetables because of their carbohydrate content. That's a real tradeoff.

If you've tried strict keto and felt worse, this middle-ground approach is worth exploring. Many women find it more effective long-term because it's sustainable and doesn't carry the hormonal complications.

Who Should Be Most Cautious with Keto

Strict ketogenic eating carries meaningful risks for some women in perimenopause that outweigh the potential benefits.

If you have a history of disordered eating, the restrictive nature of keto can activate old patterns. The extreme food rules and the categorization of foods as strictly allowed or not allowed are a particularly high-risk framework for anyone with that history.

If you're under significant chronic stress (from work, caregiving, poor sleep, or ongoing life circumstances), adding the cortisol load of ketosis is likely to make things worse rather than better.

If you have thyroid issues or are already experiencing significant fatigue, brain fog, or cold sensitivity, keto can intensify these symptoms. Get thyroid labs done before starting and recheck them after three months.

If you're very active and doing high-intensity exercise regularly, strict keto can impair performance and recovery. Low-carb is workable with proper planning; strict keto is harder to combine with intense training.

How to Approach This Decision

Keto isn't a universally good or bad choice for perimenopause. It's a tool that works well for specific situations and backfires in others.

Before starting, get baseline labs: fasting glucose, fasting insulin, thyroid panel, and a lipid panel. Recheck them after two to three months. This gives you objective data rather than relying entirely on how you feel, which can be hard to interpret when many things are changing at once.

Start with a modified low-carb approach (not strict keto) for four to six weeks before deciding whether to go lower. Many women find the modified version adequate and skip the more extreme restriction entirely.

Track your symptoms carefully. PeriPlan's symptom tracking can help you see whether changes in your eating pattern are helping or worsening your specific experience over time.

This content is for informational purposes only and does not replace medical advice. Always consult your healthcare provider about your specific situation.