Our Science and Methodology
Nutrition Built on Evidence. Not Guesswork
At Fettle, every recommendation is grounded in established nutritional sciencce and refined through real-world use.
We don't believe in rigid plans, extreme diets, or one-size fits all formulas.
We believe nutrition should adapt as your body and habits change - and that requires more tha a static calculator.
Our Science and Methodology
Nutrition Built on Evidence. Not Guesswork
At Fettle, every recommendation is grounded in established nutritional science and refined through real-world use.
We don't believe in rigid plans, extreme diets, or one-size fits all formulas.
We believe nutrition should adapt as your body and habits change - and that requires more tha a static calculator.
Our Science and Methodology
Nutrition Built on Evidence. Not Guesswork
At Fettle, every recommendation is grounded in established nutritional sciencce and refined through real-world use.
We don't believe in rigid plans, extreme diets, or one-size fits all formulas.
We believe nutrition should adapt as your body and habits change - and that requires more tha a static calculator.
Foundational Principles
Our Guiding Principles
Before we explain how Fettle works, it's important to udnerstand what guides every decision we make.
Adapt with Time
Nutrition should adapt over time
Your body is not static.
Your calorie and macro needs change as you lose fat, gain muscle, or alter your activity. Any system that doesn't adapt will eventually fall out of sync.
Trends matter
Trends matter more than single data points
Daily weight, calorie intake, or activity levels fluctuate naturally.
Fettle focuses on patterns and trends over time — not individual days — to make smarter, safer adjustments.
Sustainability
Sustainability beats extremes
Short-term restriction often leads to long-term failure.
Fettle is designed to:
Avoid extreme calorie deficits
Protect metabolic health
Support long-term adherence
Progress should feel manageable — not punishing.
Foundational Principles
Our Guiding Principles
Before we explain how Fettle works, it's important to udnerstand what guides every decision we make.
Adaption over time
Trends matter
Sustainability
Nutrition should adapt over time
Your body is not static.
Your calorie and macro needs change as you lose fat, gain muscle, or alter your activity. Any system that doesn't adapt will eventually fall out of sync.
Foundational Principles
Our Guiding Principles
Before we explain how Fettle works, it's important to udnerstand what guides every decision we make.
Adaption over time
Trends matter
Sustainability
Nutrition should adapt over time
Your body is not static.
Your calorie and macro needs change as you lose fat, gain muscle, or alter your activity. Any system that doesn't adapt will eventually fall out of sync.
Macro Calculation
How Fettle calculates your nutrition
Fettle’s engine combines established formulas with adaptive logic to create personalised, evolving targets.
Macro Calculation
How Fettle Calculates Your Nutrition
Fettle’s engine combines established formulas with adaptive logic to create personalised, evolving targets.
Step 1: Baseline energy Needs
We start by estimating your baseline energy expenditure using clinically validated equations widely used in nutrition and healthcare.
These calculations consider:
Height
Weight
Age
Sex
Activity Levels
This provides an initial estimate of your resting and daily energy needs.
Step 2: Activity & Lifestyle Adjustment
Your baseline needs are then adjusted based on your reported activity levels and lifestyle.
This helps estimate your Total Daily Energy Expenditure (TDEE) - the number of calories your body burns on an average day.
Step 3: Goal-specific Adjustments
Based on your goals (for example fat loss, maintenance, or muscle gain), Fettle applies structured adjustments to your calorie target.
These adjustments are designed to:
Support progress
Minimised unnecessary fatigue
Avoid unsafe or overly aggressive targets
Macro vs Calories
Protein, Fat, & Macro Allocation
Calories alone don't tell the full story.
Fettle calculates macronutrients with specific safeguards in place.
Macro vs Calories
Protein, Fat, & Macro Allocation
We partner with organisations and individuals who care about evidence, sustainability, and real-world impact - not quick wins or gimmicks.
Protein
Protein targets are calculated to:
Support muscle retention or growth
Improve satiety
Protect metabolic health
Protein is prioritised, especially during fat-loss phases.
Protein
Protein targets are calculated to:
Support muscle retention or growth
Improve satiety
Protect metabolic health
Protein is prioritised, especially during fat-loss phases.
Carbohydrates
Carbohydrates (carbs) targets are set after protein and fat needs are met.
This allows flexibility while ensuring energy levels are supported appropriately.
Carbohydrates
Carbohydrates (carbs) targets are set after protein and fat needs are met.
This allows flexibility while ensuring energy levels are supported appropriately.
Fats
Dietary fat is never allowed to drop below minimum safe levels.
Adequate fat intake is essential for:
Hormonal health
Nutrient absorption
Overall wellbeing
Fats
Dietary fat is never allowed to drop below minimum safe levels.
Adequate fat intake is essential for:
Hormonal health
Nutrient absorption
Overall wellbeing
Adaptive Technology
Why Fettle recalculates every week
Most nutrition apps stop here.
Fettle doesn't.
Every week, Fettle reviews your progress and adapts your targets accordingly.
Macro vs Calories
Protein, Fat, & Macro Allocation
Calories alone don't tell the full story.
Fettle calculates macronutrients with specific safeguards in place.
Protein
Protein targets are calculated to:
Support muscle retention or growth
Improve satiety
Protect metabolic health
Protein is prioritised, especially during fat-loss phases.
Fats
Dietary fat is never allowed to drop below minimum safe levels.
Adequate fat intake is essential for:
Hormonal health
Nutrient absorption
Overall wellbeing
Carbohydrates
Carbohydrates (carbs) targets are set after protein and fat needs are met.
This allows flexibility while ensuring energy levels are supported appropriately.
Adaptive Technology
Why Fettle recalculates every week
Most nutrition apps stop here.
Fettle doesn't.
Every week, Fettle reviews your progress and adapts your targets accordingly.
How Fettle uses BMI
BMI: useful context, not the full picture
BMI is often misunderstood.
BMI is used as a screening and context tool - not a diagnosis. It helps provide an initial frame of reference, but it does not:
Distinguish between fat and muscle
Account for fat distribution
Reflect individual body composition.
That's why Fettle never relies on BMI alone.
How Fettle uses BMI
BMI: useful context, not the full picture
BMI is often misunderstood.
BMI is used as a screening and context tool - not a diagnosis. It helps provide an initial frame of reference, but it does not:
Distinguish between fat and muscle
Account for fat distribution
Reflect individual body composition.
That's why Fettle never relies on BMI alone.
How Fettle uses BMI
BMI: useful context, not the full picture
BMI is often misunderstood.
BMI is used as a screening and context tool - not a diagnosis. It helps provide an initial frame of reference, but it does not:
Distinguish between fat and muscle
Account for fat distribution
Reflect individual body composition.
That's why Fettle never relies on BMI alone.
Fettle's foundation
Evidence-led, not trend driven
These foundations shape every recommendation inside Fettle.
Fettle is built using:
We deliberately avoid:
Clinically validated nutrition formulas
Fad diets
Evidence based macronutrient guidelines
Extreme restrictions
Established principles by healthcare & sports nutrition professionals
One-size-fits-all-rules
Fettle's foundation
Evidence-led, not trend driven
These foundations shape every recommendation inside Fettle.
Fettle is built using:
Clinically validated nutrition formulas
Evidence based macronutrient guidelines
Established principles by healthcare & sports nutrition professionals
We deliberately avoid:
Fad diets
Extreme restrictions
One-size-fits-all-rules
Data Trends
Using insights responsibly
We partner with organisations and individuals who care about evidence, sustainability, and real-world impact - not quick wins or gimmicks.
Fettle's Purpose
What this means for you
To improve accuracy and understand broader nutrition patterns, Fettle may analyse insights processed in an anonymised, aggregated form.
Fettle handles the complexity in the background
So you can focus on eating well and staying consistent
- without overthinking it.
Staying consistent
No daily perfection required - Fettle looks at trends, not single days
Eating better
Clear guidance that fits your goals, preferences, and real-world habits.
Making progress without stress
Progress is measured over time, with adjustments made carefully and gradually.
Data Trends
Using insights responsibly
We partner with organisations and individuals who care about evidence, sustainability, and real-world impact - not quick wins or gimmicks.
Fettle's foundation
Evidence-led, not trend driven
These foundations shape every recommendation inside Fettle.
Fettle is built using:
Clinically validated nutrition formulas
Evidence based macronutrient guidelines
Established principles used by healthcare & sports nutrition professionals
We deliberately avoid:
Fad diets
Extreme restrictions
One-size-fits-all-rules
Data Trends
Using insights responsibly
To improve accuracy and understanding nutrition patterns, Fettle may analyse insights processed in an anonymised, aggregated form.
Fettle's Purpose
What this means for you
To improve accuracy and understand broader nutrition patterns, Fettle may analyse insights processed in an anonymised, aggregated form.
Fettle handles the complexity in the background
So you can focus on eating well and staying consistent
- without overthinking it.
So you can focus on eating well and staying consistent
- without overthinking it.
Eating better
Clear guidance that fits your goals, preferences, and real-world habits.
Clear guidance that fits your goals, preferences, and real-world habits.
Staying consistent
No daily perfection required - Fettle looks at trends, not single days
No daily perfection required - Fettle looks at trends, not single days
Making progress without stress
Progress is measured over time, with adjustments made carefully and gradually.
Progress is measured over time, with adjustments made carefully and gradually.
How Fettle Works
A final word of trust
Nutrition is personal
Health is sensitive
That's why Fettle is built with restraint, responsibility and transparency at its core.
We believe the best systems are the ones you don't have to think about - they simply adapt and support you over time.
How Fettle Works
A final word of trust
We partner with organisations and individuals who care about evidence, sustainability, and real-world impact - not quick wins or gimmicks.
Macro Calculation
How Fettle calculates your nutrition
We partner with organisations and individuals who care about evidence, sustainability, and real-world impact - not quick wins or gimmicks.
Step 1: Baseline energy Needs
We start by estimating your baseline energy expenditure using clinically validated equations widely used in nutrition and healthcare.
Step 2: Activity & Lifestyle Adjustment
Your baseline needs are then adjusted based on your reported activity levels and lifestyle.
Step 3: Goal-specific Adjustments
Based on your goals (for example fat loss, maintenance, or muscle gain), Fettle applies structured adjustments to your calorie target.