Quick answer: No — being a normal weight doesn’t mean you’re metabolically healthy. A significant number of slim, active people are insulin resistant without knowing it, often because they do plenty of cardio but little to no strength training — muscle is one of the body’s main sites for glucose disposal. The good news: it’s highly reversible once identified, usually through blood markers like HbA1c rather than anything visible.
I was at my medical school reunion last night—Class of 2001. It was a genuinely wonderful evening and well attended. Faces some of whom I hadn’t seen in 25 years, people I’ve actually known for over 30 years when you include the time at medical school itself. Within minutes, it was as if no time had passed. And yet, of course, time had passed. There was an unspoken but unmistakable sense that everyone was quietly taking stock of one another—how we’ve aged, how life has treated us. Some people looked remarkably unchanged. Others… less so.
Very sadly one of our year-group is no longer with us, and another (who was there despite being in pain) has metastatic cancer and probably not long to live. A stark reminder that we are no longer spring chickens.
What was universal, though, was a shared sense of being worn down. The pressures of modern medicine, the NHS, family life—nearly everyone had children now, most approaching GCSEs and A-levels. Strikingly, across all the conversations I had, only one child was planning to go into medicine! A fair few of my co-graduates had left clinical medicine to do something else. That probably says quite a lot. It also makes me worry about what medicine will look like when I get old and need a good doctor!
It also got me thinking about something else: how deceptive appearances can be when it comes to health. One of the most common misconceptions I see in clinic is this:
“I’m a healthy weight, so I must be metabolically healthy.”
How can you look healthy but still be insulin resistant?
Unfortunately, that’s simply not true. There is often a hidden problem: insulin resistance in normal-weight individuals. We tend to associate pre-diabetes and insulin resistance with being overweight. And while excess weight is certainly a major driver, it’s not the whole story. A significant number of people who are: normal weight, physically active and eating what appears to be a “good” diet can still be metabolically unhealthy. What’s happening under the surface is that the body becomes less sensitive to insulin. Glucose isn’t handled as efficiently, and over time, blood sugar levels creep up, often silently.
How do you know if you’re insulin resistant?
So how to we know? The most common marker is HbA1c (haemoglobin A1c), which is a blood test that gives an average blood glucose level over the preceding 2–3 months. It’s not the only clue however, other useful markers include:
- Triglycerides (often elevated)
- HDL cholesterol (often low)
- Triglyceride:HDL ratio (a useful proxy for insulin resistance)
- High-sensitivity CRP (hs-CRP) (a marker of low-grade inflammation)
Individually, these can be subtle. Together, they can paint a much clearer picture. Crucially, you can feel completely well and still be metabolically unwell. Let me give you a real world example from a few weeks ago in my clinic. I saw a lady in her early 60s who hadn’t seen me for several years, and in that time had continued to look after herself well. She’s exactly the sort of person most would assume is in excellent health:
- Normal body weight
- Regularly active
- No significant past medical history
- No strong family history of diabetes
So she was understandably shocked when a routine GP health check showed she was pre-diabetic. Her first reaction was disbelief: “That can’t be right.”
But it was.
And importantly, nothing obvious had “gone wrong”. No dramatic weight gain, no major lifestyle change. Potentially a key issue? She did a lot of cardiovascular exercise—but no strength training at all.
Why Muscle Matters
Skeletal muscle is one of the body’s main sites for glucose disposal. The more metabolically active muscle you have, the more glucose you can absorb and the more insulin-sensitive you tend to be. If muscle mass is relatively low, even in someone who looks slim, glucose handling can be impaired. So paradoxically, you can be slim, fit-looking and active…but still insulin resistant. The word ‘active’ is also so highly variable in it’s meaning and perception. Many people consider themselves to be active but in reality don’t exert themselves sufficiently to be optimal. Don’t get me wrong, ‘active’ is better than sedentary, but my favourite barometer (and I’ve said this before) is to ask ‘when did you last sweat during exercise?’. Clearly for some people due to injury, disability or illness this may be challenging or even impossible but for most it’s a good question to ask yourself.
We often use body mass index as a metric of health but it falls short in many areas. BMI tells you nothing about: muscle mass, fat distribution or visceral fat (the metabolically active fat around organs). Two people with identical BMIs can have completely different metabolic risk profiles. If you really want to understand body composition, the gold standard is something like a DEXA scan, which can differentiate lean mass, fat mass and visceral fat. This is often far more informative than weight alone.
What can you do about insulin resistance?
All well and good, but what can you do about it? The encouraging part of this story is that insulin resistance is highly reversible, but the approach depends on the individual.
If you’re normal weight:
- Prioritise strength/resistance training (2–3 times per week)
- Focus on increasing lean muscle mass
- Ensure adequate protein intake
- Maintain regular physical activity
If you’re overweight:
- Address energy balance (caloric intake vs expenditure)
- Aim for sustainable weight loss
- Combine aerobic exercise + resistance training
For everyone:
- Optimise sleep
- Reduce ultra-processed foods
- Consider time-restricted eating (in appropriate individuals)
- Monitor key blood markers over time
The take-home message today is what you see in the mirror is only part of the story. You can look healthy, but metabolically be on a very different trajectory.
The good news? This is not a fixed state. It’s dynamic, and in most cases, reversible. Sometimes it just requires looking a little deeper, and making a few targeted changes. If you would like help with this, get in touch for a review.
Seeing old friends last night was a reminder that ageing is inevitable—but how we age is not entirely out of our control. Some of that comes down to luck, some down to the genetic hand we were dealt, but much of it comes down to what’s happening beneath the surface, often long before anything becomes visible, and that’s where understanding your metabolic health really matters.