What Did The Researchers Mean By A High-Protein Diet?

Most of the higher-protein diets included in this review provided approximately:

• 30% of total energy from protein
• 30% from fat
• 40% from carbohydrates

The comparison diets generally provided approximately:

• 15% of total energy from protein
• 30% from fat
• 55% from carbohydrates

One study instead prescribed around 1.5 to 2 grams of protein per kilogram of body weight each day.

The research was not examining an all-protein or zero-carbohydrate diet. It compared a moderately higher-protein, lower-carbohydrate eating pattern with a more conventional balanced diet.

The Clearest Benefit Was Lower Fasting Insulin

Compared with balanced diets, higher-protein diets produced a greater reduction in fasting insulin.

Fasting insulin reflects how much insulin the body needs to release to manage blood glucose when you have not recently eaten. When insulin remains elevated, it can signal that the body is working harder to keep blood sugar stable.

This matters in PCOS/PMOS because high insulin levels can contribute to:

• Increased androgen production
• Irregular ovulation
• Difficulty managing appetite and cravings
• Increased fat storage
• Greater long-term metabolic risk

These findings show that increasing protein can support insulin regulation, even when weight loss is similar.

Insulin Resistance Also Improved

The higher-protein diets also produced a modest improvement in HOMA-IR, a calculation commonly used to estimate insulin resistance.

However, the results varied considerably between studies, and much of the overall improvement was influenced by one trial. This finding is therefore less consistent than the reduction in fasting insulin.

The research supports higher protein as one useful option for improving insulin regulation, rather than a strategy that will affect every woman with PCOS/PMOS in exactly the same way.

Some Benefits Became Clearer Over Time

When the researchers examined study length, higher-protein diets lowered fasting insulin more clearly in studies lasting 12 weeks or longer.

In studies lasting eight weeks or less, the difference between higher-protein and balanced diets was not statistically significant.

This suggests that consistent protein intake over time is important for seeing the full metabolic benefits. It also reinforces why dietary changes should not always be judged after only a few days or weeks.

More Protein Did Not Automatically Mean More Weight Loss

Higher-protein diets were not significantly better than balanced diets for reducing:

• Body weight
• Body mass index
• Waist circumference
• Waist-to-hip ratio

Both types of diets supported weight loss when energy intake was reduced, but increasing the proportion of protein did not create a clearly greater effect.

This is an important finding because it separates metabolic improvements from changes on the scale.

A dietary approach can support insulin regulation even when it does not produce greater weight loss.

Total Energy Intake Still Played An Important Role

The higher-protein and balanced diets generally contained comparable amounts of energy.

Because both groups followed similar calorie targets, the researchers concluded that total energy intake had a greater influence on weight loss than the exact balance of protein and carbohydrates.

Protein still supports fullness, muscle maintenance and dietary consistency, but this review did not show that increasing protein alone guarantees greater weight loss.

Why Protein Supports Insulin Regulation

The researchers identified several possible reasons higher-protein diets improved fasting insulin.

Protein and amino acids support insulin clearance, which is the process through which insulin is removed from the bloodstream once it has completed its job.

Higher-protein diets also usually contain less carbohydrate. This reduces the amount of glucose entering the bloodstream and can improve the body’s sensitivity to insulin.

Protein also helps maintain lean muscle tissue. Muscle plays an important role in glucose regulation because it provides a major place for glucose to be stored and used.

Protein Supports Fullness And Dietary Consistency

Protein requires more energy to digest than carbohydrate or fat and increases the release of hormones involved in fullness.

These effects support:

• Feeling satisfied after meals
• Reducing hunger between meals
• Maintaining steadier energy
• Following a dietary pattern consistently
• Preserving lean muscle during weight loss

Because the diets in these trials were carefully matched for energy intake, the review could not fully determine whether higher protein would naturally lead people to eat less when they were free to choose how much food they consumed.

Blood Cholesterol And Triglycerides Were Mostly Unchanged

Overall, higher-protein diets were not significantly better than balanced diets for improving:

• Total cholesterol
• LDL cholesterol
• HDL cholesterol
• Triglycerides

Triglycerides improved more with higher-protein diets in some shorter studies, but this was not seen consistently in the longer trials.

Higher protein should therefore be viewed as one part of a broader approach to cardiovascular health, rather than a stand-alone strategy for improving cholesterol.

The quality and sources of protein, fats and carbohydrates remain important.

Higher Protein Did Not Directly Change Reproductive Hormones

The higher-protein diets did not produce significant overall changes in:

• Total testosterone
• DHEAS
• Free androgen index
• Sex hormone-binding globulin

This shows that increasing protein alone was not enough to create measurable changes in androgen levels during these relatively short studies.

However, improving insulin regulation remains relevant to reproductive health because elevated insulin can stimulate the ovaries to produce more androgens.

Longer studies are needed to determine whether these metabolic improvements translate into changes in hormones, ovulation or cycle regularity over time.

A Small Rise In Fasting Glucose Needs Context

The analysis found a small increase in fasting glucose in the higher-protein groups compared with the balanced-diet groups.

This was mainly seen in studies lasting eight weeks or less. In studies lasting 12 weeks or longer, there was no significant difference between the diets.

The increase was small, and fasting glucose is influenced by many factors. The researchers cautioned against interpreting it in isolation, particularly because fasting insulin improved at the same time.

This mixed result highlights the need for more long-term research.

The Findings Apply Most Strongly To Women With A Higher BMI

Almost all the studies included women classified as having overweight or obesity. Only one study did not restrict participants according to body mass index.

The findings are therefore most relevant to women with PCOS/PMOS who also have insulin resistance, elevated insulin or a higher body weight.

More research is needed to understand whether women with lean PCOS/PMOS experience the same benefits.

What About Safety?

None of the included trials reported serious adverse events from the higher-protein diets.

Protein intakes of approximately 30% of total energy, or 1.5 to 2 grams per kilogram of body weight per day, appeared generally safe within these short-term studies.

However, the interventions lasted no longer than 16 weeks, so the review cannot confirm long-term safety.

Anyone with kidney disease, a history or risk of kidney stones, or another medical condition affecting protein requirements should seek individual guidance before substantially increasing their protein intake.

This Is Not Evidence That Carbohydrates Need To Be Eliminated

The higher-protein diets still provided approximately 40% of their energy from carbohydrates.

The findings do not support removing carbohydrates completely. Instead, they show that adjusting the balance of a meal to include more protein and slightly less carbohydrate can support insulin regulation.

A practical approach includes building meals around:

• A meaningful source of protein
• High-fibre carbohydrates
• Plenty of vegetables
• Supportive fats

The overall quality and sustainability of the eating pattern remain important.

What does this mean for Protein and PCOS/PMOS?

This review shows that higher-protein diets offer an additional metabolic benefit for women with PCOS/PMOS, particularly by lowering fasting insulin.

Eating more protein was not significantly better for weight loss, abdominal fat, cholesterol or reproductive hormones when compared with a balanced diet containing the same amount of energy.

This highlights an important point. The benefits of nutrition are not always visible through body weight alone.

A higher-protein meal pattern can support insulin regulation even when the number on the scale does not change more quickly.

At the same time, protein is not a complete strategy on its own. A strong dietary approach includes adequate protein alongside fibre-rich carbohydrates, supportive fats and a broad range of nutrient-dense foods.