Embarking on a weight management journey or striving to maintain a healthy physique? The key could lie in understanding the relationship between Body Mass Index (BMI) and longevity.
This article meticulously explores the optimal BMI range associated with a prolonged, healthy life, based on an array of scientific studies. Unravel the facts about how your body weight and BMI can significantly influence your health and lifespan.
With a focus on achieving and maintaining the best BMI for longevity, this guide empowers you with the knowledge to make informed decisions on your path towards a healthier, extended life.
Through a blend of compelling data and practical advice, you’ll be well on your way to embracing a weight that not only enhances your vitality but also propels you towards a future of sustained health and longevity.
- Association of BMI with Overall and Cause-Specific Mortality
- Limitations of Body Mass Index
- BMI and Non-communicable Diseases and Injury Risk
- Specific Mortality Outcomes
- BMI and Heart Disease Risk
- How Much Longer Will You Live?
- It Starts with Satiety
- Calorie Restriction with Optimal Nutrition
- What Can You Do?
The data is from a study of 3.6 million adults in the UK looking at the relationship between body mass index (BMI) and your risk of dying from various causes. You can read the full study here for all the details and methodology.
The first chart shows BMI vs hazard ratio for men and women, showing men have the lowest risk of dying from any cause at a BMI of around 26. Women seem to have a slightly wider range before risks related to obesity start to increase. But to the left, women also have a higher risk of dying sooner if they’re underweight.
When the study authors broke the data down by age, they saw that for people under 50, the optimal BMI is around 23. As we age, the optimal BMI increases to around 25 once you’re over 80.
So, if you’ve reached 80, being a little bigger is not as big of a deal. This is likely because older people often suffer from sarcopenia (i.e., loss of muscle mass). A separate study of 350 old Italians (80 to 102 years old) found that people who had sarcopenia were 3.67 times more likely to die in the next ten years if they had sarcopenia.
So eating enough, particularly protein, to maintain muscle becomes more critical. However, if you’re obese and under 50, you’ve got a higher chance of dying from any cause in the coming years. Before 50, we need to work to be lean and strong. Afterwards, the focus turns to maintaining our muscle to prevent becoming weak and frail.
Limitations of Body Mass Index
Before we go on, it’s worth explaining BMI, its limitations and what it looks like.
BMI is commonly used for health statistics, mainly because it’s easy to track.
All you need to calculate your BMI is weight and height.
BMI is your weight (in kg) divided by your height squared (in metres). Most electronic scales will calculate your BMI, but you can calculate yours here. You can also use the BMI calculator to determine the weight you need to achieve for a certain goal BMI.
While simple, the significant downside of BMI is that it doesn’t account for people who might have more muscle but still be relatively lean. It would be great to have large datasets for body fat % to see how it aligns with longevity and disease risk, but we don’t.
If you’re doing resistance training and have more muscle than average, you can give yourself a little leeway and increase your BMI target, but the general principles still stand.
Being big isn’t necessarily healthy, even if you’re jacked and lean. There are many anecdotal stories of bodybuilders taking steroids and injecting insulin who get big but die young of a heart attack or some other organ failure because they’ve overloaded their system for too long trying to get too big.
A good way to cross-check your BMI is your waist-to-height ratio. As shown in the chart below, a waist-to-height ratio of around 0.5 is also a pretty healthy place to be.
A fasting glucose of less than 100 mg/dL or 5.6 mmol/L is a good cross-check. A lower fasting glucose indicates that you’re below your Personal Fat Threshold and the energy from your diet isn’t overflowing into your bloodstream.
In terms of body fat %, 25% for women and 15% for men is generally considered to be a pretty healthy place to be.
BMI and Non-communicable Diseases and Injury Risk
This next chart shows the BMI vs hazard ratio data based on:
- all-cause mortality (i.e., your risk of dying of any cause),
- communicable diseases (e.g., infections etc.),
- non-communicable diseases (e.g., diabetes, heart disease, cancer etc.), and
- injuries and external causes.
The relationship between BMI and infectious diseases (second chart from the left) is the most pronounced, with a sweet spot around 27. Being above this point aligns with diabetes and other diseases related to energy toxicity. However, being too lean also leaves you with less energy to empower your immune system to fight off the infection.
The relationship with non-communicable diseases (e.g., heart disease, stroke, cancer, etc.), which are responsible for 74% of all deaths worldwide, is still very strong, with the lowest risk at a BMI of around 25.
But it’s also important to note that being too lean or frail (i.e., anorexic) is not ideal. The chart in the far right shows frail people with a BMI of less than 28 are much more prone to accidents that can end their life.
Most of the research in longevity and calorie restriction is based on c-elegans worms and rodents in captivity where they are not exposed to risk of falling or infection. But free-living humans all too often fall, break a hip and never leave the hospital system, often dying of a post-operative infection or complication due to the medication.
According to a 2019 study in Acta Orthopaedica, the one-year mortality after a hip fracture is 21% for those whose fracture is surgically repaired. However, if the fracture is not repaired, the one-year mortality is about 70%.
So, especially as you age, it’s important to be as robust as possible. If you’re frail, your risk of falling and breaking something that will eventually lead to your death increases steeply.
Longevity guru Peter Attia highlights that you need to train for the last decade of your life. If you want to be able to care for yourself and play with your great-grandkids, you need to start ‘training’ for that now. The strength you gain in your 30s and 40s is an investment account you get to use later.
Specific Mortality Outcomes
The data gets fascinating when we look at the relationship between BMI and your risk of dying of specific causes.
Having a healthy body weight aligns with a lower risk of dying of just about anything, including:
- most cancers,
- endocrine issues,
- cardiovascular disease,
- respiratory infections, and even
Take a moment to check out the chart above and see if you can spot the causes of death that do not increase with obesity. The handful of causes of death that do not align with obesity include:
- prostate cancer,
- interpersonal violence, and
The paper doesn’t detail mechanisms, but we could hypothesise that having enough energy and nutrients is important for mental function. If you’re unable to nourish your brain, your mental health isn’t going to be so great. Getting enough energy and all the nutrients you need is critical for optimal mental health and happiness.
BMI and Heart Disease Risk
Next, let’s double-click on heart disease risk.
As shown in the charts below, a strong correlation exists between your weight and your risk of heart disease, the leading cause of death in the developed world.
Unfortunately, discussion around heart disease risk quickly gets complex. It often revolves around warnings to AVOID certain things in food and managing the different types of fat in your blood (e.g., LDL, HDL, ApoB etc.).
Until 2015, the US Dietary Guidelines recommended avoiding cholesterol, but they finally concluded that dietary cholesterol doesn’t affect your heart disease risk. Now the Dietary Guidelines focus on avoiding saturated fat while prioritising unsaturated fat.
But the reality is, excessive intake of any energy source will lead to obesity, including unsaturated fats.
We can easily get caught up in avoiding ‘bad’ nutrients, like fructose, sugar or starch, but they’re really all just energy sources that we need a little less if we want to lose body fat.
Our satiety analysis shows, because it is such a dominant energy source in our modern food system, monounsaturated fat is statistically correlated with eating more, especially when combined with starch in ultra-processed food.
While saturated fat is also a source of energy, going out of your way to avoid it tends to lead to eating more because it makes it harder to get bioavailable protein, which is the biggest positive factor in the satiety equation.
As we can see from the charts above, the most effective way to manage your blood pressure or heart disease risk is not to be too fat. To do this successfully over the long term, you need to find a way of eating that provides greater satiety so you’re not as hungry.
Our satiety analysis has repeatedly shown that, regardless of your eating preferences, eating less requires that we prioritise getting more of all of the essential nutrients — like amino acids, minerals and vitamins — your body requires within your energy budget.
But simply restricting calories is hard in real life. So, to eat less, you need to start by prioritising optimal nutrition.
For more details, see:
- Why the Dietary Guidelines are Broken (And How to Fix Them)
- Monounsaturated Fat: Is It So “Good” After All?
- The Food Satiety Index Score (Updated 2023)
- What is Nutrient Density (and Why It Matters)?
How Much Longer Will You Live?
I recently found this chart in The Longevity Diet by Professor Roy Walford’s daughter, Lisa Walford, and Brian Delaney. They extrapolated data from calorie-restricted mice and other organisms to humans. Based on the data from laboratory mice, they hypothesised that humans might be able to live past 150 years if they could severely restrict their calorie intake.
Unfortunately, I think this might be a bit over-optimistic. We don’t have any human data showing this age extension level due to calorie restriction. Even the data from monkeys is questionable — all it showed conclusively was that monkeys live longer if they eat less processed food, but monkeys eating their natural diet tend to live just as long when eating to satiety.
Similarly, laboratory mice aren’t a great model for human longevity. Given the opportunity, rodents will eat continually and get fat, especially when fed obesogenic rat chow, which is a processed blend of fat and carbs similar to our modern ultra-processed human foods. It makes sense that eating less of this trashy diet helps the mice live longer, but it’s probably not applicable to humans striving for optimal nutrition.
As mentioned earlier, we need to remember that free-living humans often die due to infection and falls, so being frail because we’re malnourished isn’t necessarily optimal.
For a more realistic estimate of how much longer we’ll live, we can look back to the UK data analysis of 3.6 million people, which shows that, on average, morbidly obese men are likely to die 9.1 years earlier than men at a healthy weight. On the flip side, note that underweight women are likely to die 4.5 earlier than those at a healthy weight.
This data doesn’t consider fitness or diet. You’ll likely do better than average if you’re fit, active, robust and well-nourished.
It Starts with Satiety
When you search Google for the best diet for longevity, you’ll be bombarded with many conflicting opinions and expensive supplements.
- Is vegan better than carnivore?
- What about the Mediterranean diet?
- What supplements should you take?
- Is NR better than NMN?
But the data shows that maintaining healthy body composition is the most important thing you can focus on. Not many of us today are at risk of being underweight, but a growing majority are above the healthy weight range.
Our research and analysis have shown that prioritising what your body needs increases satiety and helps you achieve a healthy body weight. Once you nail this, you won’t need to worry too much about anything else. You can get on with living your life rather than micromanaging the minutia.
Calorie Restriction with Optimal Nutrition
Part of the impetus to start Optimising Nutrition was my fascination with Calorie Restriction with Optimal Nutrition, spearheaded by Professor Roy Walford and his experience in Biosphere 2 (1991 – 1993).
But when I analysed the meals recommended by Walford and the “CRONies”, I found that not many were not particularly nutrient dense. So, I designed a quantitative approach people could use to get all the essential nutrients without excess energy. Regardless of our beliefs or preferences, we all need enough of the essential nutrients from our food.
More than one hundred and fifty thousand days of data from Optimisers also shows that foods and meals that provide more of all the essential nutrients with less energy provide greater satiety and enable people to maintain a lower energy intake with less energy.
What Can You Do?
The reality is that calorie restriction is hard, so few people succeed long-term, especially without prioritising optimal nutrition.
Many people interested in longevity turn to fasting. Unfortunately, without adequate focus on protein and nutrients when we eat, this can lead to a loss of lean mass and increased frailty.
In Data Driven Fasting, we use your glucose as a fuel gauge to guide your eating routine to ensure you actually need to refuel before you eat while emphasising getting adequate protein when you eat. This promotes greater satiety and more stable blood glucose and ensures that you’re losing fat and not your precious lean mass.
Similarly, in our Macros Masterclass, we guide Optimisers to dial back their energy from fat and/or carbs while prioritising protein and nutrients to increase satiety and ensure you’re not losing precious lean mass.
Finally, in our Micros Masterclass, we guide Optimisers to get more of their priority nutrients from foods and meals they love to eat. We always find that once people learn to cram more of the nutrients they need into their energy budget, their cravings settle down. They are satisfied with fewer calories without relying on supplements — calorie restriction with optimal nutrition!
As shown in the chart below, people with a higher Diet Quality Score consume much less energy.
How Can I Calculate if I Am Getting Enough Nutrients?
Nutrient Density Starter Pack
We’re eager to make the process of Nutritional Optimisation as simple as possible. So, to help you increase your intake of all the essential nutrients when you join our free Optimising Nutrition Community, you’ll get a starter pack that includes:
- Food Lists – optimised for each essential nutrient, goals, preferences and conditions.
- The Healthiest Meal Plan in the World – see what a week of nutrient-dense eating looks like.
- Recipes – check out samples of each of our NutriBosoter recipe books.
- 7-Day Nutrient Clarity Challenge – identify your priority nutrients and the foods and meals that contain them.