Most diets fail because they are built to be finished, not kept. A crash diet cuts intake so hard that hunger, fatigue and muscle loss make it impossible to hold, and when it ends the old routine and the weight both come back. So why do diets fail? Not for lack of willpower. Mr PT Fitness is a private home studio at 35 McIntosh Road, Dee Why, run by Matt Reilly, a personal trainer with 10+ years' experience, and the most common story new clients tell is the same one: lost weight fast, regained it, tried again. The fix is a slower, smaller change you can keep, with a commonly used target of about 0.5 to 1 percent of bodyweight a week.
Why do crash diets fail?
Crash diets fail because they ask for a change too big to keep, so they only work while you can tolerate them. Once hunger, low energy or a busy week breaks the rules, intake returns to where it was, and nothing about the underlying routine has changed.
A crash diet usually looks like one of three things: a very low calorie target, cutting out a whole food group, or replacing meals with shakes or juice. All three can make the scales drop quickly. None of them teach you what to eat on a Tuesday night when you are tired and there is nothing in the fridge.
That is the real gap. Fat loss is decided by energy balance over weeks and months, which is covered in detail in energy balance explained. A crash diet creates a big deficit for a short time. A plan that works creates a smaller deficit for long enough to matter, and then holds the result.
Most people who come to the studio after a crash diet did not lack discipline. They followed a plan that was designed to be finished, and it finished.
What happens when the deficit is too aggressive?
A very large deficit tends to bring more hunger, lower energy and a bigger share of muscle in the weight you lose. You also tend to move less without noticing, so the deficit shrinks while the diet feels harder. The scale can still drop, but more of what it shows is water, food volume and muscle than you want.
- Hunger goes up. Eating far less than usual is associated with stronger appetite and more food thoughts, which makes every social event and every evening harder.
- Energy goes down. Training quality drops, and everyday movement such as walking, standing and fidgeting tends to fall as well. That unplanned drop in movement eats into the deficit.
- Muscle is at risk. Losing weight fast with little protein and no strength training means a larger share of the loss can come from muscle rather than fat. Muscle is what keeps you strong and shapes how you look at a lower weight.
- The early drop is misleading. The first few kilos on a very low intake are largely water and stored carbohydrate, which come back quickly when normal eating resumes.
None of this means the body is broken. It means a very large deficit is expensive, and most people cannot afford that cost for long.
| Crash diet | Sustainable approach | |
|---|---|---|
| Rate of loss | Fast early, then stalls or reverses | About 0.5 to 1 percent of bodyweight a week |
| Food rules | Cut out whole foods or meals | Keep normal foods, adjust portions |
| Protein and training | Often low protein, little or no strength work | Protein at each meal, strength training two to three times a week |
| Hunger and energy | High hunger, low energy | Manageable hunger, energy to train |
| End point | Stops on a date, old habits return | Moves into planned maintenance |
Why do you regain the weight?
Weight comes back after a crash diet mainly because the eating habits that produced it come back. The diet changed what you ate for a few weeks without changing the routine underneath, so when it ended, intake returned to the old level.
There are a few things that make the rebound feel sudden. The water and stored carbohydrate lost early on return within days of eating normally, which can look like a kilo or two of fat overnight. It is not. After weeks of restriction, appetite also tends to run high, so the first few weeks off a diet often involve eating more than before it started.
If muscle was lost along the way, you are also a little smaller and weaker than when you began, which means slightly less energy used each day and less capacity to train. That is one reason regain can land as more fat and less muscle than you started with.
The pattern then repeats: regain, frustration, a stricter diet. Each round makes the next one feel harder. Breaking that cycle is less about finding a better diet and more about stopping the need for one.
Tired of starting again every January?
Bring your diet history to a free 15-minute consult at the Dee Why studio. We will work out a pace and a routine you can actually hold. Book here or call 0422 745 334.
What is the slower approach that actually holds?
Aim for a moderate deficit that loses roughly 0.5 to 1 percent of bodyweight a week, eat protein at every meal, lift weights two to three times a week, and keep your daily steps up. That combination protects muscle and keeps hunger manageable, so you can keep going for months instead of weeks.
For an 80kg person, that pace is about 0.4 to 0.8kg a week. It feels slow in week two. By week twenty it is 8 to 16kg, and most of it can be fat rather than water and muscle.
- Moderate deficit: small changes such as smaller portions of the energy-dense foods, fewer liquid calories and a planned treat rather than a banned one. No food group has to disappear.
- Protein at each meal: protein is filling and helps hold on to muscle while you lose fat. How much protein you need covers simple daily targets.
- Strength training: two to three sessions a week gives your body a reason to keep muscle while you eat a little less.
- Steps: daily walking adds to the deficit without adding much hunger. Dee Why beach, the lagoon and the Curl Curl headland all make easy loops.
Expect the scales to move unevenly. A flat week followed by a bigger drop is normal. Judge the trend across three or four weeks, not day to day, and use tape measurements and how your clothes fit alongside the number.
How do you diet once, not forever?
Treat fat loss as one phase with a clear end, then move into a planned maintenance phase where you eat a bit more and keep the habits you built. The goal is to finish dieting, not to start again next year.
That means the habits used during the diet need to be ones you would keep anyway: protein at meals, regular strength training, daily steps and a sensible approach to eating out. If a habit only makes sense while dieting, it will not survive maintenance.
When you reach your goal, or after 12 to 16 weeks of steady loss, increase food gradually rather than all at once. Keep training at the same frequency. If your weight holds steady for a few weeks, that is your new maintenance, and it is a skill in its own right.
If you want this set up around your week, the nutrition plan from $120 sets a pace, protein targets and a maintenance plan, alongside 1-on-1 training from $50 a session or small group from $25 a person. It is general guidance within a personal trainer's scope, not a dietitian service.
If you have a diagnosed condition such as diabetes, take regular medication, are pregnant or breastfeeding, or have a history of disordered eating, speak to your GP or an Accredited Practising Dietitian before changing how you eat. They can set a safe rate of loss for your situation.
General information, not individual medical or dietary advice. See your GP or an Accredited Practising Dietitian (APD) for your situation.
Frequently asked questions
Why do I always regain weight?
Usually because the diet ended and the old routine came straight back. A crash diet changes what you eat for a few weeks without changing the habits underneath, and it often costs muscle and raises hunger on the way. When the rules stop, intake returns to where it was and the weight follows.
Are crash diets ever okay?
For most people, no. Very low calorie diets do exist, but when they are used for health reasons they are run under medical supervision with a GP or Accredited Practising Dietitian. A self-directed crash diet from social media is a different thing, and it tends to end in regain rather than lasting fat loss.
How fast should I lose weight?
A commonly used guide is about 0.5 to 1 percent of bodyweight a week, which is roughly 0.4 to 0.8kg for an 80kg person. Faster than that usually means a deficit that is hard to hold, more muscle lost, and more hunger. Your GP can advise on a safe rate for your health.
Lose it once and keep it off
Free 15-minute consult at the Dee Why studio. We will set a realistic pace, a protein target and a training routine you can keep through maintenance. Clients come from Dee Why, Brookvale, Curl Curl and Collaroy.