Okay, I'm going to stick my neck out and give advice. And you might not want to hear it, in which case read no further, or you might disagree, in which case tell me and I'll back down, argue or acknowledge different ways of looking at the same thing, or read it and think that maybe I've got a point, whether you intend to be *inspired* by it or not.
If you're saying 'I really should lose some weight', you're not going to.
If you're saying 'I must go on a diet' you probably won't.
If you're saying 'I'm dieting from now onwards, and no, I won't have pudding, thanks', you might.
If the doctor says 'You need to lose weight' you will genuinely try to.
If you quietly decide that enough is enough, you're doing it from now on and you don't care how long it takes or how hard it is, then you probably will give it your best shot.
So, let's say that you have definitely decided to get fitter, lose weight or both. The decision isn't worth a small, hard, shit. Nor is joining a gym or buying a bike. You've got to use it. Consistently. Quite possibly, forever.
I have done it both ways (that is, dieting with and without extra deliberate exercise), so I know that you can lose weight without taking any more exercise, and as you do so, you will move about faster, so that will help. But exercise tones you up and you will, immensely gratifyingly, look thinner than you actually are, so taking some exercise is a Pretty Good Thing, and it helps with the dieting.
Before you go all out with a heavy-duty exercise programme, consider what you want more: - to lose weight or to become fit and/or muscular. Because the latter doesn't necessarily mean the former. A friend of mine, told she had to lose weight before having an operation, exercised like mad but didn't eat differently, and she hardly lost anything. They operated anyway and she feels better, but she's still fat. She now thinks it's impossible to lose weight. Exercise tones and fittens, but doesn't make you lose weight.
Exercise does raise your metabolism, so you're more likely to lose weight if you diet as well. So, if you want to lose weight, exercise enough to raise metabolism and no more. Muscle-building makes you weigh more. And if you're not dieting too, you'll use the increased muscle as an excuse (which may well be true) for not losing weight.
So, you decide to go to the gym/go running/walk to work/cycle/swim. You are full of determination and enthusiasm. You work hard and lose several pounds in the first weekend/week/month. You multiply that by 52/12 and say that's what you'll lose by this time next year.
I'm not saying this is impossible, but it's very unlikely. Lower your expectations. Bear in mind that there will be weeks, maybe whole months, where you will be too busy or on holiday or going to parties and you will not lose any weight at all, and you may gain a couple of pounds. Even if you diet steadily, crash dieting for a year is unhealthy and leads to diminishing returns. Sure, we've all read about the people who've lost half their body-weight in a year, but they are unusual (and I'd like to see them in 5 or 10 years and see if they've kept the weight off, because I think many of them will be bigger than when they started). Most of us aren't unusual. Most of us eat a reasonable diet, with a few bad habits, and there just isn't enough to cut out to be able to lose that much without risking ill-health. Keeping up strength is important, especially when you're over 40, or have small children, or hope to have children, or have a demanding job, or don't want to risk osteoporosis when you're older, or don't want to catch every infection going. This means me and you and every other bugger.
Losing weight slowly and steadily is best and we all know that, but it's boring and a real pain to have to keep buying new clothes in a smaller size (unless you like buying lots of cheap clothes) but nevertheless, it's the most reliable way of losing weight and keeping it off. If you go on a crash diet, you may well lose weight quickly but the odds are you haven't devised a sustainable and better eating pattern and it'll all go on again as soon as you stop dieting.
10% - 15% of your body weight in a year is a really good and impressive weight loss. If you now weigh 100kg (random amount because the maths is easy), wouldn't you love to weigh 90? Or 85? So why do you think you have to lose 1 kg every week for a year? It's not on, is it? You will not lose half your body-weight. Relax. Losing 1 or 2 kg a month is superb. Even half that is good news. Especially if you've actually arrested weight gain. If you've been gaining a steady 3 kg a year for the last few years, gaining nothing is an advance. Particularly if you're fitter and healthier because you are taking some exercise and noticing what you eat.
Ach, this is too long and I've been opinionated long enough. I'll be back with the rest. And I'll still be annoyingly right.