We all have bad days where we smash every calorie in sight, but how much damage can they do?

Can One Bad Day Ruin Your Diet?

Written by Russ Howe PTI, and most recently updated 1 day ago.

5 min read

Is it true that you can ruin your whole diet with one bad day?

This is something whihc many gym-goers worry about, because it’s easy to fall off-track after a period of doing well, and the last thing we want ts to undo all of our hard dwork, right?

So I’m going to jump into the science on this topic today, and I’ll also reveal some neat strategies which my clients and I have used over the years to minimize the damage when calamity strikes.

Table of Contents

The Simple Answer Is Yes

can a cheat day ruin your diet

The simple answer is yes.

Your diet is a numbers game, so any period of over-eating has the potential to throw your numbers off course, even if it’s just one day.

However, I believe that ruin is the wrong word to use.

In my experience, this discourages people and they end up pushing the ‘fuck it button’ (where one day becomes the remainder of the week, and that’s where lasting damage is done) when, in truth, they didn’t need to panic so much.

Because the thing about games is that there’s always a way to win. That means, although you may have done some damage with a big day of unplanned eating, there are ways you can get back on track and keep progressing without this being anything more than a tiny blip in the road!

For example;

Let’s say your daily target is set to 2000 calories per day. That’s 14000 calories per week. You have a stressful day at work on Tuesday and it leads to you smashing 3000 calories of mostly junk food. If you remained on track for every other day except Tuesday, your weekly calorie intake is 15000, which works out at an average daily calorie intake of 2142, and this is why your progress might stall that particular week.

A graph showing how one day of overeating can impact your diet

The good news is these days happen to everyone (me included!), and I have three strategies you can use to get yourself back on track!

Strategy 1: The Clean Slate Method

You’ll simply put this behind you and start over tomorrow.

It sounds crazy, considering the fitness world is choc-full of douchebags who promote the idea of self-punishment and personal shame over “not wanting it bad enough”, but this is something I used to immense success with various male and female clients over the years.

Because in order for you to build a great body, you must also build a healthy relationship with food!

That means not feeling guilt, shame, or stress about the things you eat, and being strong enough to acknowledge that these days happen to everyone from time to time, then getting back to work the next day (hence the name; the clean slate method). (1, 2)

Strategy 2: Small Deficits Each Day

In situations where you are unable to use the clean slate method (i.e. you’ve got a deadline to hit and you want to undo the previous splurge to remain on track), I recommend creating small calorie deficits each day until you’ve caught back up.

You can do this by taking your total overshoot and dividing it by however many days you’d like to spread it over.

Some people prefer a more aggressive approach (i.e. they ate 1000 extra calories and they’ll undo it by going 500 calories below for the following two days), but most people see better results by spreading the load over a few more days so the deficit is smaller (i.e. 1000 extra calories is undone by eating 250 calories below for the next four days).

Either way works, and both are fine to use!

A graph showing how to catch up after going over your calories
Graph showing how to get your diet back on track after an unplanned cheat day

Strategy 3: Increased Calorie Burn

Some people prefer not to touch their diet, but rather to increase their training output for a greater calorie burn.

Like the old saying goes; “If you make a big enough fire, you can throw anything on it!”

This can definitely be done, but there are a few reasons why it’s last on my list.

The first reason is because calorie trackers are notoriously poor at doing their jobs. In 2019, a report found that they over-estimate calorie burn anywhere between 10-90% (!), so there’s no accurate way to tell when you’ve caught back up.

The second reason is because increased exercise leads to increased injury risk. Let’s face it, you’re already hitting the gym and pushing your body hard, so any additional work on top of this brings with it an additional risk factor.

The third reason is because the body can adapt to your workload over time, so this is a technique which is best used sparingly. A recent study from the University of Ottawa discovered that our basal metabolic rate (BMR) slows by around 28% when we markedly increase physical activity, and it suggested that trainees with higher amounts of body fat could see an even greater BMR adjustment, underlining the importance of high quality nutrition when trying to lose weight, as opposed to just adding more cardio. (3)


  1. Hall K. D., et al. Maintenance of lost weight and long-term management of obesity. Med Clin North Am (2018)
  2. Stewart T. M., et al. Rigid vs. flexible dieting: association with eating disorder symptoms in nonobese women. Appetite (2002).
  3. Halsey L. G., et al. Energy compensation and adiposity in humans. Curr Biol (2021).

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I’m Russ. I’ve been a personal trainer since 2002, and I own russhowepti.com.

My job is to simplify fitness for my readers.

I send out free fitness tips to over 100,000 men and women every week, all in the same no-nonsense style as the article you’ve just read, so if you enjoyed reading it be sure to jump on my email list below.

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