Look, I'm just a fat guy in the US, which is almost a bit redundant, I suppose. I'm a med student as well, and nutrition is starting to hit the medical culture in some useful ways. There's fantastic stuff looking at the relationship between the microbiome and health, especially as it relates to energy, satiation, and diet. There's a lot of information out there, though the research is still relatively new. Still, expect more of the formerly-esoteric concept of "diet" to become actual science in the next 5 to 20 years.
That said, here are a couple of basics - most of which have been mentioned throughout these replies, but bear repetition. First, as you lose weight, your caloric needs come down. Also, weight loss is ONLY about calories. Health is about quality of calories. So if you want to be both smaller and healthier, than you need fewer calories and you need them to come from healthier sources.
Unless you are an athlete or VERY physically active in some way, most of your daily calories are used just staying alive. Consider that an "average" man burns 900 to 1200 calories during 8 hours of healthy sleep, while running a mile only burns an extra 100 calories. So if you reward yourself with a PB&J sandwich after a good ride, you likely ate more calories than you burned. Food for thought, as they say.
Weight loss isn't about dieting. It's about changing lifestyles. Exercise more, eat less, eat healthy foods. Avoid processed foods. If you can't pronounce it, don't eat it. Discover vegetables and grains you've never heard of before, and consume more of them. Avoid dairy. Move every hour, even if it's just a few laps around your yard/office building/obese neighbor. Drink water, stop drinking everything else. Drink more water. Have another glass of water.
As to the rest.. fads come and go. So does weight loss, if it's based on a fad diet.