Beyond BMI
Attend any annual physical or routine health check-up, and you’re likely to be assessed first against a single measure: Body Mass Index (BMI). You step on a scale, measure your height, and receive a tidy label such as ‘underweight’, ‘healthy’, ‘overweight’, or ‘obese’.
Whilst a simple and quick measure to perform, BMI can mask deeper truths. A ‘normal’ BMI doesn’t always mean you’re in the clear health-wise, and a higher BMI doesn’t necessarily guarantee poor health across all markers. In reality, metabolic health is a multifaceted blend of blood markers, body composition, lifestyle, and more.
The Illusion of a “Normal” BMI
Despite its popularity—especially prevalent within the NHS—BMI has major blind spots:
1. It doesn’t distinguish muscle from fat. BMI lumps all weight together. Someone with a high muscle-to-fat ratio could register as ‘obese’ by BMI standards—think of Arnold Schwarzenegger in his prime. Meanwhile, another person with less muscle and more fat may register as ‘normal’ but have a significantly less healthy profile.
2. It ignores fat distribution. Visceral fat (fat stored abdominally around organs) is far more dangerous than the subcutaneous fat just under the skin. BMI can’t tell the difference. Two individuals with the same BMI can face vastly different health risks if one carries more visceral fat.
Such oversights explain why some individuals may appear lean according to BMI but still carry risky levels of visceral fat. Conversely, those labeled ‘overweight’ may in fact, be metabolically healthier than the above counterpart if they have substantial muscle mass and low visceral fat.
The concept of metabolic health is crucial because it underpins our defence against chronic illnesses like type 2 diabetes, heart disease, and certain cancers. Yet today’s ‘normal’ health ranges often come from populations already trending toward poor metabolic health, making these benchmarks less robust than we might like.
The Problem with BMI: A Flawed Metric in Isolation
Even a ‘normal’ BMI doesn’t ensure you’re metabolically healthy. Imagine a bell curve representing a population's metabolic health markers. The 'normal' range often falls in the middle, but if the overall population is already skewed toward poor health (and only progressively getting worse with time…), this 'normal' range becomes less than ideal for comparison.
Research suggests 20–30% of people within the ‘normal’ BMI range still exhibit markers typical of obesity—such as insulin resistance or elevated triglycerides. In other words, BMI alone can lull us into complacency or cause us to stigmatise unnecessarily.
Example A: Two males, each with a BMI of 25. One with ~20% body fat by measurement and a high muscle mass as indicated by a Fat-Free Mass Index (FFMI) result. The other carries ~30% body fat, predominantly in his abdomen, and a below-average FFMI. Same BMI, wildly different health outlooks.
Example B: A female labeled ‘overweight’ by BMI classification who strength trains and has excellent metabolic markers. Her higher muscle mass inflates her BMI, yet her visceral fat is low, even by athletic female standards. Asking her to lose weight to improve her BMI may require shedding muscle—something few, if any, would actively aim to do.
Over time, societal trends like increased sedentary behaviour and processed food consumption have shifted the average metabolic health markers in an unfavourable direction. This means that staying within the 'normal' range might only indicate you're average within a less-than-healthy population, not that you're truly thriving.
Defining Metabolic Health: Beyond the Averages
As mentioned within the categorisation of BMI, the typical thresholds for ‘healthy’blood pressure, lipids, and blood glucose control, often derive from average populations where many individuals are already on the path to metabolic dysfunction. These norms, whilst useful indicators, may not be optimal if you want truly robust health.
So what should be our targets should we be considering in addition to BMI?
Key Metabolic Markers:
Blood Lipids
Triglycerides: Ideal = <150mg/dl
HDL Cholesterol: Ideal = >38 mg/dl (with higher being considered better)
LDL Cholesterol: General guidelines suggest <116 mg/dl without the use of medication, however optimal levels can vary significantly between individuals and are often debated within the medical community. It is best to consult with your GP or health provider regarding your own personal LDL target."
Triglyceride/HDL Ratio: Ideal = <2
2. Blood Glucose
Fasting Blood Glucose: Ideal = <100mg/DL
HbA1c: Ideal = <5.5% (below 6% in less stringent guidelines)
3. Blood Pressure
Systolic: Ideal = <120mmHg
Diastolic: Ideal = <80mmHg
4. Inflammation
C-Reactive Protein (CRP): Ideal = <3 mg/dl (lower is considered better)
Many would argue for more stringent criteria, especially those aiming for a higher standard for metabolic health rather than simply meeting the ‘average’ of the bell curve. If we re-evaluate thresholds to more optimal levels that consider the population and societal changes that have occurred over time, we begin focusing on true risk mitigation rather than simply staying within questionable norms.
Beyond Body Weight
Understanding actual body composition (the ratio of lean mass; muscle, bone, and organs, to fat mass), not just overall body weight, offers deeper insights into the individuals health outlook. Why? because muscle is more metabolically active than fat tissue, and aids in glucose regulation, hormone balance, and calorie expenditure at rest. It has a potentially greater functional purpose.
Key Body Composition Metrics
Fat-Free Mass Index (FFMI)
FFMI indicates the amount of lean tissue (muscle mass) relative to height whilst factoring in body fat percentage. While numerous online calculators offer FFMI estimations and can be a useful starting point, it's crucial to acknowledge their potential limitations. For more accurate assessments, particularly when tracking progress, consider using methods outlined in the measurement methods section below in corroboration with FFMI.
An FFMI of >19 in males, and >16 in females are a useful starting point for comparison.
2. Body Fat Percentage
As mentioned previously, having a determinant of body fat levels can be a useful tool to consider when taken in conjunction with a BMI score, providing context where necessary in more extreme examples of increased muscle mass, or significantly reduced body fat percentage.
General recommendations to help in keeping an individual at the lower-risk bracket for many metabolic diseases would be the following; <~20% in males, <~32% in females.
3. Waist-to-Height Ratio (W:H) or Waist Circumference
A very simple metric to help in determining levels of visceral fat around the waist, is a waist-to-height target of <0.5
Likewise a waist circumference <40 inches (102cm) in males, and <35 inches (88cm) in females, can be a used as an indicator.
4. Measurement Methods
Depending on the capacity to access the needed equipment, we have tools and measurement methods available that help determine multiple measure of body composition both quickly and effectively.
Dual-energy X-ray Absorptiometry (DEXA) scans: Considered the gold standard for body composition assessments and accuracy, providing a measurement of body fat, muscle, bone, as well as estimations of basal metabolic rate (BMR) and visceral fat levels.
Bioelectrical Impedance (BIA): A more cost effective and convenient measure than DEXA, however with higher degree in variability of accuracy measurement. BIA measures how the body resists the flow of electrical current. An incredibly non-invasive way to estimate body composition, including fat mass, muscle mass, and body water.
Skin-fold Callipers: A budget friendly measurement. The accuracy of skin-fold calliper measurements heavily depends on the skill and experience of the practitioner. Therefore, seeking assessment from a trained professional is paramount for obtaining meaningful and consistent results. The resulting formulas used for estimation of overall body fat percentage lack validity, therefore the change in “raw” measure over time can be a useful tool for establishing changes in body fat percentage.
For reliable results with these tools, standardisation is key. This includes maintaining consistent hydration levels, fasting for a few hours before testing, and avoiding exercise immediately prior. Variations in these factors can significantly impact accuracy.
The Role of Lean Mass
As we’ve established, a higher lean mass improves insulin sensitivity, increases resting metabolic rate, and supports overall health. To determine an individuals metabolic health, lean muscle mass should play an important part in the measure. Resistance training and adequate protein intake therefore become a cornerstone of building or preserving muscle, especially as we age and the risk of muscle mass increases.
Beyond the Numbers: Other Key Markers and Influences
So we’ve began to establish a picture of metabolic health markers that includes BMI, blood markers than indicate metabolic syndrome (blood lipids, glucose control, blood pressure, inflammation), and emphasised the importance that overall body fat percentage, lean muscle mass, and regional distribution of body fat can play in maintaining metabolic health.
Do we have any other considerations of markers and potential influences?
Insulin Sensitivity
Insulin is a hormone that helps cells to absorb glucose. Insulin resistance is a hallmark of metabolic syndrome an precursor to type 2 diabetes. Testing fasting insulin (alongside blood glucose), or using a HOMA-IR (Homeostasis Model Assessment of Insulin Resistance) which calculates how resistant your body is to insulin, can offer a glimpse into how efficient your body manages blood sugar.
Insulin resistance is often intertwined with other metabolic dysfunctions, such as elevated triglycerides and reduced HDL cholesterol. These interconnected markers contribute to an increased risk of cardiovascular disease and type 2 diabetes.
The Gut Microbiome
Emerging research into the gut microbiome suggest it heavily influences weight management, inflammation, and metabolic function. Supporting a healthy gut microbiome involves a balanced diet rich in fibre from diverse sources like fruits, vegetables, and whole grains. Fermented foods such as yogurt, kefir, and sauerkraut can introduce beneficial bacteria. As well as incorporating prebiotics (e.g., onions, garlic, bananas) that feed existing gut bacteria. Limiting ultra-processed foods, artificial sweeteners, and excessive alcohol consumption also plays a vital role.
Lifestyle Factors
Sleep
Inadequate or poor-quality sleep disrupts hormone balances like leptin and ghrelin, driving up hunger and down regulation of metabolism.
For an extensive look at the impact of sleep on metabolic health, consider Matthew Walker’s book “Why We Sleep”.
2. Stress Management
Chronic stress elevates cortisol, impacting blood sugar, fat storage, and hunger cues.
A fantastic read into the topic is Robert Sapolsky’s “Why Zebras Don’t Get Ulcers”.
3. Circadian Rhythm
Optimising light exposure, especially by getting sunlight in the morning, helps regulate your circadian rhythm. This signals your body to be alert during the day and promotes better sleep at night. Conversely, minimising exposure to blue light from screens in the evening is also important.
Lynne Peeples’s “The Inner Clock” is a great look into these internal mechanisms.
The Role of Genetics
Whilst we no-doubt have a large amount of control over our metabolic health, certain genetic profiles do predispose individuals to insulin resistance or high cholesterol.
However, lifestyles factors and appropriate use of medication often exert powerful influence, meaning even those individuals with unfavourable risk profiles genetically can benefit dramatically from the right habits and medical support.
Lifestyle Strategies: Taking Control of Your Metabolic Health
A: Dietary Recommendations
Emphasise Whole Foods: Lean protein in sufficient quantities, healthy fats, and complex carbohydrates from fruits vegetables and whole grains.
Mindful Eating: Whether this is through the use of nutrition tracking, deliberate ‘active’ phases of attempted fat loss, controlling portions, or limiting highly-processed, calorie dense food items.
Fibre Focus: Support a healthy gut microbiome and better regulate blood sugar.
B: Exercise Guidelines
Resistance Training: In my opinion, a non-negotiable for metabolic health. Essential for building or preserving muscle mass, and highly impactful on improving insulin sensitivity.
Cardiovascular Activity: Supporting heart health through adequate daily movement (eg. step count target thresholds), and maintaining cardiovascular fitness.
Consistency over Intensity: Optimising for an exercise routine or schedule that you can stick to for the long-term rather than short-sporadic intervals followed by extended periods of inactivity, burnout, or even injury.
C: Stress Reduction Techniques
Mindfulness and Meditation: Specific mindfulness techniques such as deep breathing exercises, body scans, or guided meditations can effectively reduce cortisol levels. Apps and online resources provide accessible tools for practicing these techniques (Calm, Headspace, Waking Up).
Time in Nature: Similar in outcome to mindfulness and meditation; stress reduction, mood and concentration enhancing, lower risk of depression, sleep improvement, lowering of blood pressure…
D. Sleep Hygiene
Regular Schedule: Aim to have relatively consistent times in which you aim to both go to bed and wake up. Ensuring a sufficient window of time spent in bed to achieve your target sleep time. For example, a sleep time goal of 7hrs may require closer to an 8hr window of sleep opportunity (10pm-6am).
Bedtime Routine: Wind down from screens, low lighting, calming actives, minimise food intake and alcohol consumption in the 2-3 hours prior to bedtime.
Optimal Environment: Turn your bedroom into a metaphorical cave… cool, dark, and quiet.
The Research Gaps and Future Directions
As we began with in this article, little has been studied about those who maintain normal-to-low body fat percentages, engage in consistence resistance training, and hit optimal metabolic markers. Large scales studies just simply don’t tend to take place within ‘healthy’ populations. There is plenty therefore to discover and learn from a research perspective into how these individuals manage stressors and maintain a metabolic health equilibrium.
The Importance of Personalised Medicine
As genetic testing and biomarker technology improve, we’re seeing potential for tailored interventions. Innovations like GLP-1 medications (e.g., Ozempic, Mounjaro)also highlight how medical support can reshape metabolic health for those with specific challenges.
Conclusion: Embracing a Proactive Approach
Our reliance on BMI as a sole indicator of health has, in many ways, over-simplified a complex reality. True metabolic health is about more than just being in the ‘normal’ classification for body weight; it’s multifaceted bled of body composition, metabolic markers, and lifestyle factors.
Remember, early detection of issues like high blood pressure, insulin resistance, or unfavourable blood lipid ratios provides an opportunity to course-correct before chronic disease sets in. By focusing on consistent habits, the things we repeatedly come back to in these articles - regular exercise, nutrient-rich meals, stress management, and quality sleep - we can make huge strides towards not only the appearance on health on the surface, but truly being healthy and the core.
If you’ve been relying on BMI as your primary, or only measure of health, consider exploring the additional metrics and strategies detailed in this article. Reach out to your GP with any concerns you may have, consider the use of private blood testing to establish a baseline, consider regular body composition testing, or simply adopt a more manageable and consistent exercise routine alongside more mindful nutritional decisions.
With a proactive, holistic approach, you’ll likely be far more equipped to maintain genuine metabolic health across the lifespan.