Metabolic health
How well your body handles energy, and why most adults are further from healthy than they think.
Metabolic health describes how well your body takes in, stores and uses energy from food. When it works well, your blood sugar, blood fats and blood pressure stay in a healthy range with little effort. When it doesn't, the damage builds quietly, and it raises your risk of nearly every chronic disease in this course: heart disease, stroke, type 2 diabetes, fatty liver, kidney disease, several cancers and dementia.
It's also one of the areas where lifestyle changes work fastest.
The five markers
Doctors use five measurements to define metabolic syndrome. Having three or more means you have it. Being metabolically healthy means all five are in range without medication.
| Marker | Healthy range |
|---|---|
| Waist circumference (European adults) | Under 94 cm for men, under 80 cm for women |
| Blood pressure | Below 130/85 mmHg |
| Fasting glucose | Below 5.6 mmol/L (100 mg/dL) |
| Triglycerides | Below 1.7 mmol/L (150 mg/dL) |
| HDL cholesterol | Above 1.0 mmol/L (40 mg/dL) for men, 1.3 mmol/L (50 mg/dL) for women |
A simpler waist check: your waist should be less than half your height. A 180 cm tall person should have a waist under 90 cm.
Most people aren't there
In the United States, analyses of national health data have found that fewer than one in eight adults meet all the criteria for good metabolic health. Europe does somewhat better, but around one in four European adults has metabolic syndrome, and many more have one or two markers out of range. Being slim is no guarantee: some people of normal weight carry fat around their organs and have poor metabolic markers.
Insulin resistance: the hidden problem
When you eat, blood sugar rises and your pancreas releases insulin, which helps move that sugar into your muscles, liver and fat cells. Over years of excess energy, low activity and poor sleep, cells respond less well to insulin. Your pancreas compensates by producing more of it.
For a long time, this works: your blood sugar stays normal, but only because your insulin levels are high. This stage can last a decade or more, and standard tests often miss it, because fasting glucose is one of the last markers to change.
Ways to spot it earlier:
- HbA1c, your average blood sugar over about three months. Below 5.7% is normal; 5.7–6.4% is prediabetes.
- Fasting insulin, often not included by default but easy to request. Combined with fasting glucose it gives a score called HOMA-IR.
- The triglyceride-to-HDL ratio. A high ratio is a useful, cheap signal of insulin resistance.
- Your waist. Fat stored around the organs is the most metabolically harmful kind.
Muscle is your metabolic organ
After a meal, skeletal muscle is where most of the glucose goes. More muscle means more space to store it, and every contraction pulls glucose out of the blood, with or without insulin. That's why strength training and walking are two of the most powerful metabolic interventions there are.
- Walk after meals. Even 10–15 minutes after your largest meal noticeably lowers the blood sugar peak.
- Build and keep muscle. Two or three strength sessions a week.
- Break up sitting. A few minutes of movement every half hour improves blood sugar across the day.
What else moves it
Sleep. Even a few nights of short sleep measurably reduce insulin sensitivity in healthy young adults.
Food. More fibre, protein and whole foods; fewer sugary drinks, refined carbohydrates and ultra-processed foods. The order you eat in matters a little too: vegetables and protein before starchy foods tends to flatten the glucose curve.
Weight loss, if your waist is a red box. Losing 5–10% of body weight improves most metabolic markers. In the landmark Diabetes Prevention Program, people with prediabetes who lost about 7% of their weight and walked 150 minutes a week cut their risk of developing type 2 diabetes by 58% over three years, more than the medication group.
Alcohol. It raises triglycerides and blood pressure and adds calories. Cutting back often improves both within weeks.
Reversal is possible
Metabolic health responds quickly. Blood pressure and triglycerides can improve within weeks of changing diet, activity and alcohol. Even type 2 diabetes can go into remission for some people: in the UK DiRECT trial, almost half of participants on a structured, medically supervised weight-loss programme were in remission after a year.
Newer medications such as GLP-1 drugs can also help people with obesity or type 2 diabetes, under medical care. If you use them, prioritise protein and strength training to protect your muscle.
Continuous glucose monitors
A CGM is a small sensor on your arm that tracks glucose day and night. For people without diabetes, two to four weeks of wearing one can be a useful lesson in how your meals, sleep, stress and exercise affect you. It isn't necessary long-term, and single spikes after a meal are normal; what matters is your overall pattern.
Key numbers
5: markers that define metabolic health.
Waist under half your height: the simplest check.
58%: lower risk of type 2 diabetes with lifestyle change in the Diabetes Prevention Program.
This week
- Measure your waist and divide it by your height. Aim for under 0.5.
- Walk for 10 minutes after your largest meal every day.
- Add HbA1c and, if possible, fasting insulin to your next blood test.
In the journal
Waist, blood pressure and body fat are Foundational boxes; HbA1c, glucose and triglycerides are Advanced. If one of them is your bottleneck, "walked after my biggest meal" is a good one for your seven boxes.
Sources: Alberti et al., harmonised metabolic syndrome definition, Circulation 2009 · Araújo et al., Metabolic Syndrome and Related Disorders 2019 · Knowler et al., Diabetes Prevention Program, NEJM 2002 · Lean et al., DiRECT, The Lancet 2018 · NICE guideline NG246, waist-to-height ratio, 2022
Put this chapter into practice — The Longevity Journal