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Losing 20kg, why a check with your GP comes first

Witney Nutrition
Updated on 21 October 2026, 2 min
Losing 20kg, why a check with your GP comes first
Key points

Before trying to lose 20kg, book an appointment with your GP for a health check. Your GP checks that nothing stands in the way, adjusts your medicines if needed and gives you a reliable starting point. 20kg is about 3 stone 2lb, and that check protects the whole journey.

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In this article
  1. Why see your GP for 20kg
  2. What the check may include
  3. Preparing for the appointment
  4. After the check
  5. Starting without rushing
  6. At Witney Nutrition Club
  7. Your weight loss curve

Why see your GP for 20kg

A goal of 20kg involves your whole body. Your heart, blood pressure, blood sugar, liver and joints are all concerned. Your GP looks for anything that might explain the weight gain, such as a thyroid problem or a medicine. They also spot what needs keeping an eye on while you lose weight.

The NHS page on overweight and obesity advises seeing a GP if your BMI is in the overweight or obese range and you want help to lose weight. The same applies if you have diabetes, high blood pressure, joint pain or sleep apnoea. A GP can also refer you to local weight management programmes.

What the check may include

  • Measurements. Weight, height, waist size and blood pressure.
  • A blood test. Often blood sugar and cholesterol, sometimes thyroid or liver, depending on your situation.
  • Your medicines. Some treatments for diabetes or blood pressure need adjusting as weight comes down.
  • Your history. Past illnesses, past diets and any eating difficulties.

What is checked depends on your GP and your health. You can work out your BMI with the NHS BMI calculator before the appointment.

Preparing for the appointment

Write your questions down beforehand. Bring the list of your medicines and any old blood results. Say honestly what you eat and which diets you have tried. Your GP needs that true picture to advise you well.

After the check

Your GP will tell you whether you can start with everyday support, or whether regular medical follow-up is better. Keep your blood results. A new test a few months later can show what has improved, a kind of progress the scales never show.

Starting without rushing

The NHS suggests aiming to lose 0.5 to 1kg a week, which is 1 to 2lb. So 20kg is counted in months, not weeks. Our page on lasting weight loss explains why a steady pace holds better.

Start with the basics of healthy eating and where to start, without skipping meals. A proper breakfast, some protein at every meal and fewer sugary foods are enough for the first weeks. Our ideas for a breakfast that supports weight loss help with the morning.

At Witney Nutrition Club

Coaches trained in nutrition do not replace your GP. This article does not replace advice from your GP or another health professional. At Witney Nutrition Club, members have breakfast at the club in the morning before work. The free assessment is where it all starts.

Your weight loss curve

Enter your profile and the curve redraws straight away.

You are
Ideal, 0.5 to 1 kg a week Too fast, muscle loss Median curve Journey, plateaus and regains

At the median pace, it would take about 11 weeks to lose 8 kg. At the gentlest pace, about 4 months.

The benchmark most often given for lasting weight loss is 500 g to 1 kg a week. That is the ideal zone of the chart. Above 1 kg a week on a regular basis, the body draws on its muscles as much as on its fat. That is the hatched zone.

An indicative projection. Every journey is personal and results vary from person to person. The calculation runs on your device, nothing is saved or sent. Over 65, talk to your doctor first.

How this curve is calculated

The top edge of the zone matches 500 g a week, the gentlest pace. The bottom edge matches 1 kg a week, the risk threshold.

The first weeks go faster, mostly water, then the pace slows. After 40, the median curve slows gradually, because metabolism slows. For the same effort, a man usually loses weight a little faster than a woman.

The journey curve adds plateaus of a few days and small regains, as in real life. It does not predict your own journey.

This advice is general. It does not replace medical advice.

Further reading

For day to day support, see the healthy eating programme.