Insulin Resistance, Obesity, and the Loss of Metabolic Reserve

Insulin resistance is often described as a blood sugar problem.

In the usual explanation, the body becomes less responsive to insulin, glucose becomes harder to control, and the risk of type 2 diabetes increases. This explanation is important, but it may not be complete.

A recent review by Boccardi and Sinclair, titled Rethinking insulin resistance in aging: A reserve-oriented clinical framework, offers a broader view. The authors suggest that, especially in aging, insulin resistance may reflect a loss of metabolic reserve across the whole body — not just a defect in glucose handling.

This means insulin resistance may tell us something deeper: the body may be losing its ability to adapt, recover, repair, and use energy flexibly.

Insulin resistance is more than a glucose number

The review explains that insulin resistance in aging involves many connected systems, including:

• skeletal muscle

• adipose tissue

• mitochondria

• inflammation

• hormones

• brain metabolism

This broader view is important because many people with insulin resistance do not only have abnormal blood sugar or insulin markers. They may also experience fatigue, poor exercise tolerance, reduced muscle quality, increased abdominal fat, chronic low-grade inflammation, brain fog, mood changes, or slower recovery.

In this sense, insulin resistance may be a warning sign that the body’s reserve is being stretched.

Why muscle matters

One of the most important points in the review is the role of skeletal muscle.

Muscle is not only for movement. It is a major site for glucose use, energy production, amino acid storage, and metabolic flexibility. Healthy muscle helps the body handle nutrients more effectively.

With aging, inactivity, stress, inflammation, poor sleep, or illness, muscle may lose both quantity and quality. This can make it harder for the body to use glucose, burn fat efficiently, and recover after stress.

This helps explain why a person can have excess fat but still have poor metabolic reserve. The body may be storing energy, but not using that energy effectively for strength, repair, and recovery.

Fat tissue is not passive storage

The review also reminds us that adipose tissue is not just a storage depot.

Fat tissue, especially visceral or abdominal fat, can become metabolically active. It may release inflammatory signals, affect hormones, and contribute to insulin resistance. When fat tissue becomes dysfunctional, lipids may also accumulate in the liver, muscle, and other tissues.

This shifts the question from:

“Why did this person store too many calories?”

to a deeper question:

“Why is the body directing energy toward storage instead of using it efficiently for repair, movement, and recovery?”

This is where the review aligns with our broader Exposure-Related Obesity perspective.

How this connects with Exposure-Related Obesity

Exposure-Related Obesity, or ERO, is a developing framework that asks whether some obesity patterns may reflect more than calorie excess alone.

Calories still matter. Energy balance still matters. But the body is not a simple calculator. It is an adaptive system that responds to diet, stress, sleep, inflammation, hormones, medications, environmental exposures, and life transitions.

From this perspective, some obesity phenotypes may develop when the body is repeatedly pushed into a state of stress adaptation, but does not fully return to recovery.

Possible contributors may include:

• poor diet quality

• excess or poorly timed energy intake

• low protein or micronutrient adequacy

• chronic psychological stress

• insufficient sleep

• circadian disruption

• chronic inflammation

• environmental toxicants

• endocrine disruption

• certain medications

• aging, menopause, illness recovery, or prolonged caregiving stress

These factors do not all act in the same way. But they may converge on shared systems that regulate insulin sensitivity, inflammation, mitochondrial function, appetite, fat storage, and recovery.

From storage to recovery

The key clinical lesson is that obesity care should not focus only on weight reduction.

Weight matters, especially when excess fat increases cardiometabolic risk. But weight alone does not tell us whether the body has good muscle reserve, low inflammation, flexible metabolism, restorative sleep, or the capacity to recover.

A person may lose weight but remain metabolically fragile if sleep, stress, inflammation, muscle loss, or nutrient insufficiency are not addressed.

This is why a recovery-focused approach is important.

Instead of asking only:

“How do we reduce weight?”

we can also ask:

• How do we improve metabolic flexibility?

• How do we preserve or rebuild muscle?

• How do we improve sleep and circadian rhythm?

• How do we reduce chronic inflammatory burden?

• How do we support mitochondrial function?

• How do we help the body move from defense back toward recovery?

What this means in clinical practice

A more complete clinical approach may include looking beyond BMI and calories.

Depending on the person, useful areas to assess may include:

• waist circumference or waist-to-height ratio

• body composition, including muscle and visceral fat

• strength and functional capacity

• fasting insulin, glucose, HbA1c, triglycerides, and HDL cholesterol

• inflammatory markers when appropriate

• sleep quality

• stress burden

• medication history

• dietary quality, protein intake, and meal timing

• possible sources of chronic inflammation or environmental exposure

This does not mean everyone needs every test. It means the clinical picture should be interpreted as a pattern, not just a number.

A more compassionate model

This reserve-oriented view also helps move the conversation away from blame.

If insulin resistance and some obesity patterns reflect reduced metabolic reserve, then the solution is not simply to tell people to “try harder” or “eat less.”

The better question is:

What is keeping this body in a state of defense, storage, and poor recovery?

For some people, the answer may involve diet. For others, it may involve sleep, stress, inflammation, muscle loss, medications, hormonal changes, or environmental exposures. Often, it is a combination.

Takeaway

The review by Boccardi and Sinclair gives us an important message:

Insulin resistance may not only be a problem of glucose control. It may also be a signal that the body is losing metabolic reserve.

The ERO perspective extends this idea to obesity care.

In some people, obesity may not only mean that excess energy has been stored. It may also reflect a body that is struggling to recover, rebuild muscle, resolve inflammation, and use energy flexibly.

This does not replace standard obesity or diabetes care. But it adds a useful layer.

The goal is not only restriction.

The goal is restoration.

This article is intended for public education and does not replace individualized medical care. The ERO perspective is a developing framework and should not be interpreted as a formal diagnostic category.

Boccardi, V., & Sinclair, A. J. (2026). Rethinking insulin resistance in aging: A reserve-oriented clinical framework. Ageing Research Reviews, 119, 103180. https://doi.org/10.1016/j.arr.2026.103180