Diet questions
How long should you try a diet?
Give a sensible diet about 8 to 12 weeks before deciding whether it works for you. The first week or two are misleading, because early weight changes are mostly water. Stop sooner if you feel unwell, and change course if you are miserable well before then.
Why the first two weeks don't tell you much
When you cut back on carbs or calories, your body uses up some of its stored carbohydrate, called glycogen, which is held with water. That can show up as a drop of a few pounds on the scale in the first week. It feels great, but most of it is not fat.
The reverse happens too. Many people feel worse before they feel better: a dull headache on day three of keto, afternoon tiredness while getting used to smaller portions, or a hungry evening when a time-restricted eating window is new. These early effects often settle within a week or two.
A rough timeline
| When | What you can judge |
|---|---|
| Week 1-2 | Can you shop, cook and eat this way? Any side effects? |
| Week 4 | Hunger, energy and sleep have usually settled. Is the routine getting easier? |
| Week 8-12 | A fair picture of weight trend, how your clothes fit and whether you still like the food |
| Month 3-6 | A good time to recheck blood pressure, cholesterol or blood sugar with your doctor if those were goals |
At a safe pace of around 0.5 to 1 kg (1 to 2 lb) a week, 12 weeks is enough to see a clear trend even with normal day-to-day ups and downs.
Track more than the scale
Write down a few things once a week, on the same day and at the same time:
- Weight, or a weekly average if you weigh daily.
- Waist measurement.
- Hunger between meals, on a simple 1-to-5 scale.
- Energy and sleep.
- How much time you spend thinking about food.
- What the week's shopping cost.
A diet that takes off weight but leaves you exhausted, obsessed with food and over budget is not working, whatever the scale says.
When to stop early
Stop and talk to a doctor if you have dizziness or fainting, heart palpitations, ongoing diarrhoea or constipation, or low blood sugar symptoms such as shaking and sweating, especially if you take diabetes medicine. The same goes if you notice bingeing, guilt around food or a return of old eating-disorder thoughts.
Related questions
Why has my weight loss stalled after a month?
Early water loss has ended and fat loss is slower, so the scale moves less. Look at the trend over three or four weeks rather than day to day before deciding anything has stalled.
Is it OK to switch diets if I'm not enjoying mine?
Yes. Enjoying the food is one of the best predictors of sticking with it. Keep the habits that worked and try a pattern that fits your tastes better.
How long do keto side effects last?
The tired, headachy feeling often called keto flu usually eases within a week or two. Drinking enough fluid and getting enough salt and other electrolytes can help.
Keep reading
Before you start, read what makes a diet sustainable and whether you need a dietitian. The glossary covers ketosis, electrolytes and a calorie deficit. For a steady plan, see how to spot a safe weight-loss program and how to choose a diet.