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The metabolic test your doctor isn’t ordering

Fasting insulin predicts dysfunction years before your blood sugar rises

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May 26, 2026 8:00am EDT

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FROM DR. BERZIN:

Fasting insulin is one of the earliest and most actionable indicators of how your body is managing blood sugar. Starting at age 25, we recommend testing it alongside glucose, hemoglobin, A1c, and other metabolic markers, because patterns in these levels will give you a longitudinal picture of your health.

Keep reading for blood sugar balancing tips for every decade of your adult life.

— Robin Berzin, MD, Founder & CEO, Parsley Health

Most labs don’t fully assess your metabolism’s efficiency. Longevity Labs do.

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Condition Spotlight: Metabolic Syndrome

Metabolic syndrome is a cluster of interconnected risk factors that, together, significantly raise your risk of type 2 diabetes, heart disease, and stroke. It's diagnosed when three or more of the following are present: elevated blood sugar, high triglycerides, low HDL cholesterol, high blood pressure, and excess abdominal fat.

In conventional medicine, these markers might be addressed in isolation. A cardiologist checks your lipids. A PCP flags your blood pressure. Nobody connects the pattern until metabolic dysfunction progresses to type 2 diabetes. At Parsley, we look at all the ways that blood sugar, hormones, inflammation, and lifestyle interact to identify your risk early. With the right data and plan, you can shift your trajectory long before it becomes a diagnosis.

Read More: Early Signs of Diabetes in Women and Prevention Tips

Insulin Balance by the Decade: Take Action in your 20s, 30s, 40s, 50s, 60s and Beyond

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Metabolic health changes as you age, even with healthy habits in place. Rather than attempting to halt natural shifts, we encourage you to work with your body’s evolving needs to maintain insulin balance through every stage. Here are some things to watch for.

In your 20s
Your insulin sensitivity is probably at its highest, but lifestyle patterns may erode it. Run a baseline fasting insulin test by age 25 to establish your starting point and catch fluctuations before they compound.

Take note of: irregular energy, sugar cravings, and reliance on caffeine to get through the day.

Read More: What Does Sugar Do to Your Brain

In your 30s
Insulin resistance might start to become symptomatic. Prioritize nutrition; anchor meals around protein, fiber, and healthy fats to stabilize blood sugar. Test fasting insulin alongside glucose and A1c for a clearer picture.

Take note of: unexplained midsection weight gain, difficulty losing weight, energy crashes, unrelenting premenstrual symptoms, and irregular cycles

Read More: Common Causes and 4 Ways to Get Rid of Hormonal Belly Naturally

In your 40s
As your estrogen begins to fluctuate due to perimenopause, insulin resistance might emerge or worsen. A fasting insulin panel alongside sex hormones, cortisol, and thyroid markers will give you a full picture of what's driving what. Focus on building muscle with 2-4 strength training sessions each week, and try to go to sleep and wake up around the same time each day.

Take note of: shifting weight distribution, disrupted sleep, and increased carb sensitivity

Read More: Biohack Your Way to Better Sleep

In your 50s
Naturally decreased muscle tissue can impair your body’s ability to manage blood sugar. Regularly test and track fasting insulin, lipids, and inflammatory markers. Keep strength training; studies show that it improves insulin sensitivity regardless of weight loss. Go for compound movements that engage large muscle groups, paired with plenty of dietary protein to support muscle maintenance.

Take note of: rising cholesterol, blood pressure changes, and increased fasting glucose

Read More: How Does Exercise Affect Female Hormones?

In your 60s
The cumulative effect of lifelong metabolic patterns will be visible in your labs and how you feel. Blood sugar variability tends to increase, and can be closely tied to cognitive and cardiovascular health. Pay close attention to fasting glucose trends over time to understand how specific foods, sleep, and stress are affecting you. Aim for stability: daily movement, balanced meals, and maintained muscle mass.

Take note of: fatigue, brain fog, and increased variability in energy and appetite

Read More: Eat to Beat Brain Fog

In your 70s (and beyond)
After age 70, the goal is to preserve independence and cognitive clarity. Research consistently shows that people who reach 100 tend to maintain lower fasting insulin and better glucose tolerance than their peers. Post meal walks of 10 to 15 minutes can blunt post-meal blood sugar spikes. Combine these with light resistance training, regular provider check-ins, and longitudinal lab tracking.

Take note of: unintentional weight loss, low energy, changes in appetite

Read More: How Do I Manage My Blood Sugar?

BIOMARKER SPOTLIGHT

Fasting Glucose

This commonly ordered lab measures your baseline blood sugar after an overnight fast. It provides a real-time snapshot of how your body is managing glucose in that moment, which can be a useful early warning system for prediabetes, diabetes, and insulin resistance. But like most single markers, it tells an incomplete story.

Why we test glucose + insulin
We test fasting glucose alongside fasting insulin to get the output (the blood sugar level itself) and the effort (how hard your pancreas is working to maintain it). For example, normal fasting glucose with elevated fasting insulin could indicate that the body is working harder than it should be — a quiet sign of dysregulation.

Why patterns matter more than single readings
Fasting glucose can climb over time while still landing in the “normal” range. This points to changes worth investigating in nutrition, stress, sleep, and hormonal balance.

Glucose is included alongside 80+ other biomarkers in every Longevity Labs panel.

Metabolic syndrome is preventable and reversible. We’ll help you find and treat it.

Check your fasting insulin

What We're Taking (and Why)

Vanilla Rebuild Clean Protein Powder

Protein slows the absorption of carbs, blunts those post-meal blood sugar spikes, and supports muscle mass. These effects are important whether you're in your 30s building healthy metabolic habits or in your 50s actively working to preserve muscle and insulin sensitivity.

Each serving of our clean protein powder delivers 26g of protein from a blend of pea protein isolate, rice protein concentrate, L-glutamine, taurine, and glycine for a more complete amino acid profile. It's formulated without gluten, dairy, soy, GMOs, or added sugar, so it supports blood sugar stability rather than disrupting it.

Shop Power Proteins

“This has been my morning go-to for a few years now. It makes getting protein first thing easy, which is key for me.” - Ellen A.

What members are saying:

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“I have been trying to find answers for 7+ years as to why I am fatigued all of the time and struggle with brain fog and weight gain. I received more answers in one session with my Parsley Doctor and Health Coach than I ever have meeting with traditional doctors."

- Stacey R., Parsley Health Member

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