The Science
How we estimate
your journey.
MEDCO+ uses established metabolic science to give you a realistic, personalised estimate of what's achievable. Every figure below is grounded in peer-reviewed research and validated equations — not guesswork.
Important: these are informational estimates only. They help you understand what's realistic. They are not a prescription, a dose recommendation, or a guarantee. All treatment and dosing decisions are made independently by your GMC-registered doctor.
*The 60-minute prescription turnaround is the expected target when a clinician is available. It is not guaranteed and is subject to queue volumes and clinician availability. Average response times may be longer outside of standard hours.
1. Your energy baseline
We start by estimating how much energy your body uses. Your Basal Metabolic Rate (BMR) — the calories you burn at rest — is calculated using the Mifflin–St Jeor equation, the most accurate validated formula across diverse populations:
BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × age) + s
s = +5 for men, −161 for women
We then adjust for how active you are to find your Total Daily Energy Expenditure (TDEE) — the calories you burn in a full day:
TDEE = BMR × activity factor
1.2 (sedentary) to 1.55 (moderately active)
2. The energy of weight loss
Roughly 7,700 kcal of energy deficit equals about 1 kg of body fat (Wishnofsky, 1958). This lets us estimate the weekly deficit needed to reach a goal in a given timeframe:
Weekly change = (current weight − target weight) ÷ weeks
Weekly deficit needed ≈ weekly change × 7,700 kcal
This is how we tell you whether a goal is comfortably realistic, ambitious, or faster than is typically safe — so you have honest expectations from day one.
3. What the medication adds
GLP-1 treatments such as Mounjaro (tirzepatide) work by reducing appetite, slowing gastric emptying, and supporting better blood sugar control — which makes a sustained calorie deficit far more achievable. The effect is dose-dependent, demonstrated in the SURMOUNT-1 clinical trial (Jastreboff et al., New England Journal of Medicine, 2022):
| Tirzepatide dose | Avg. body weight reduction | Duration |
|---|
| 5 mg / week | ~15% | 72 weeks |
| 10 mg / week | ~19.5% | 72 weeks |
| 15 mg / week | ~20.9% | 72 weeks |
These are trial averages, not predictions for any individual. Your doctor decides if, and at what dose, treatment is appropriate — always starting low and titrating gradually.
4. How treatment is dosed
Mounjaro is never started at a high dose. Treatment begins at 2.5 mg weekly and increases gradually — typically by 2.5 mg every four weeks — only as tolerated, up to a maximum of 15 mg. The pace of any increase is a clinical judgement made by your doctor based on how you respond, never by a formula or a deadline.
5. Variability — why we give ranges
Everybody responds differently. Clinical trials show individual results vary by around 3–6% of body weight around the average. Factors include adherence, baseline metabolism, existing conditions, diet, and activity. That's why we always present a range, not a single number — honest estimation over false precision.
Worked example
Starting weight 95 kg, goal 75 kg, over 20 weeks.
Required average loss ≈ 1.0 kg/week. Combined with a clinician-managed treatment plan, this sits within mid-range clinical outcomes and is considered realistic — with an expected variability of ±3–6% body weight. Your doctor would design a safe, gradual plan to support this.
References
- Jastreboff AM et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine.
- Mifflin MD et al. (1990). A new predictive equation for resting energy expenditure. American Journal of Clinical Nutrition.
- Wishnofsky M (1958). Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition.
- Hall KD et al. (2011). Quantification of the effect of energy imbalance on bodyweight. The Lancet.
- Pontzer H et al. (2021). Daily energy expenditure through the human life course. Science.
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