One thing I tend to notice is people saying they're eating "pretty healthy" but then their serving sizes are quite large. It's so easy to overeat and not even realise it, and if you are trying to lose weight eating more calories than your body needs is still going to eventually cause you to gain weight. The sizes that restaurants feed you is not a single serving! I've done up a little downloadable chart that has a bunch of pretty common foods and how much of them actually qualifies as a serving.
Click on the image below for it to open full resolution.
How many of these should you eat per day? Vegetables: 5 servings Fruit: 2 servings Milk, yoghurt, cheese, nut milks: 2.5 servings (4 if you're over 50 years of age) Grains: 4-6 servings Meat, eggs, nuts, seeds: 2.5-3 servings Junk food (this includes alcohol too): 0-2 servings Servings can be higher for more active individuals.
Did any of the serving sizes surprise you?