One pizza won't make you fat, just as one salad won't make you thin.
Technically, you could eat nothing but pizza and still lose weight as long as you are in a calorie deficit, however, I don't advise this. Consistently eating this type of food will do sweet FA for your health. A diet that mainly consists of saturated fats, high salt, highly processed ingredients can lead to atherosclerosis (arteries clogged with plaque), which in turn can eventually cause heart attacks and stroke. Nobody wants that, surely!?
On the flip side, eating a diet full of nutrient dense foods, fresh fruit and veg, lean protein, grains, nuts and seeds to name but a few will keep your arteries healthy and ensure the blood can flow freely through them, reducing the risk of coronary heart disease.
But don't be fooled, just because a food is more nutritious, doesn't mean it's devoid of calories, just take the avocado for example, people go nuts over 'avo on toast' these days because it's seen as a healthy option, but this still has around 265 calories per slice.
Losing weight comes down to consistently being in a calorie deficit and therefore being aware of the amount of calories you need for this to happen as well as knowing how many are in your food. If you don't know this, how can you know if you're actually in a calorie deficit?
Awareness will help you achieve the results you desire.
If this has got you thinking and you want to lose weight but don't know where to start, don't be afraid to reach out and send me an email, I'll get back to you with details of how I can help you.