Life is a complicated exercise made up of simple equations.
For example, weight and health are a function of simple equations of diet and lifestyle. Nothing simpler. If you want to gain weight, consume more calories than you burn, every day. If you want to lose weight, burn more calories than you consume, every day. If you want to maintain weight, equalize the two roughly.
Except that the numbers in the equation are made up of multiple variables, many of which change throughout our lives and can be hard to quantify. Metabolism, thyroid function, family history all play a part. So do food allergies and reactions, and the type of diet you have. Diets higher in fat, or carbohydrates, or protein, change your body chemistry and affect how you handle resources and energy. Whether the 300 calories you burn in your workout are aerobic or anaerobic, whether you're building muscle or burning fat, it all plays into that equation. If the disparity between calories taken in and calories burned is too great OR too small, then your metabolism compensates and the desired effect doesn't happen. Behind that simple "(calories in - calories out)/3500 = weight change in pounds" equation is an entire life's work of understanding your own body and what you want it to do for you.
'Being healthy' is another simple thing. Eat a variety of foods that provide you the resources you need, get regular moderate exercise and plenty of restful sleep, drink lots of water, see your physician for an annual checkup or if anything about your health needs managing. Very simple, and if we all did that, we'd all be healthy regardless of our waist sizes. All the mysterious miracle "eat this and don't eat that and never touch this food and if you only eat sugar while standing on one foot it doesn't count" diet voodoo in the world can't even begin to touch the benefits of giving your body the right amounts of rest, resources, and exertion.
But then come the variables. What are the resources you need and how do you prioritize them? If you need more iron, do you get it from leafy green vegetables that are loaded with fiber and other nutrients but don't supply much protein, or meat that supplies protein with added fat and no fiber? Vitamin D in your milk, or from sunshine? What if you're allergic or sensitive to a food that provides a critical nutrient? Do multivitamins supply the things you need, or just pass through your system undigested? How do chronic health conditions, from celiac disease to fibromyalgia to insomnia, play into the balance of eating, exercise, and sleep? Is your thrice-weekly strength training a sustainable lifelong practice? How can you afford to see a doctor regularly or even in an emergency if you have no health insurance and can't afford an office visit?
Habits also play a huge part in how we live and in our general health. It is my habit to have a cup of coffee every morning. This decreases the absorption of my iron supplement, so on days I take iron, I have to delay my cup of coffee until mid-morning and start my day with orange juice. It is my habit to come home from work and relax with my cats for a while to unwind, but after doing that it's really hard to get motivated to go exercise. If I want to get in the active time I have to come home, immediately change, work out, and then pet the cats. Because it's important to me to stay active and healthy, I have had to figure out ways to balance what I need to do with what I want to do.
That is, at the heart of it, what solving the equation comes down to. Would I be healthier if I didn't eat cookies for breakfast as often as I do, and if I never blew off working out to read a book and drink a glass of wine instead? Probably, and I'd definitely be thinner, but I wouldn't be as happy. Meeting specific and often socially-imposed criteria about the shape of my body is less important to me than enjoying the life experience that body is having, so there's a variable in my personal equation that says, "Is that fun, or at least not terribly annoying?" If the answer is no, there has to be a significant payoff for me to make that choice. A lot of folks see my insistence on honoring that variable as weak-willed or lazy, and they make assumptions about me based on the importance I place on living joyfully.
The biggest problem with all this is that people confuse 'simple' and 'easy'. The simple thing is the easy thing if it also happens to be the thing that fits in with your needs, practices, and priorities, but that's rarely the case. Consequently, some people look at others and see them struggling with what appears, from the outside, to be an easy fix. Without understanding the variables affecting another person's experience, the inability to separate 'simple' and 'easy' can lead to frustration, and even to judgment, bigotry, and discrimination.
We look at an obese person or someone with a chronic illness, and think, "How unhealthy. Why can't she just exercise and eat right?" and we make assumptions about her -- usually that her evenings consist of sitting on the sofa eating ice cream right out of the container. But there are things we don't know, can't know: what her metabolism is like, whether she lives in a food desert and can't afford fresh fruits and vegetables, whether she has a chronic health condition that makes exercise difficult, whether she's perfectly happy looking the way she does, whether she's quite healthy and as active as she wants to be, or whether decades of being pressured to look and act and eat and live a certain way have left her depressed or suffering from an eating disorder.
At its heart, fat hate and fat prejudice (and most ableist prejudices) come from the assumption that other people can and should solve their equations with your variables. They should be able to shoehorn their experience and their priorities into a set of life choices that matches what the mythical "everyone" wants. They should place the same value on what really is a marketing-driven artificial standard of 'healthy living' and strive to operate within it. The media machine that's worked so well to convince us that somewhere there is one perfect diet or exercise plan that will render everyone identically thin and healthy (and Dr. Oz will tell you all about it after this message from our sponsors) has also convinced us that living outside of an artificially established 'normal' body image is not only a conscious choice, but a lazy, despicable, self-destructive one.
Many of my friends are frequently trying to 'get healthier', with varying degrees of success. The ones who succeed aren't the most dedicated or the strongest-willed. They're the ones who work to understand as many of their own variables as possible, from the biology (family history, metabolism) to the limitations (allergies, mobility concerns, medical issues) to the geographical (availability of food resources and activity centers) to the emotional (habits, body image satisfaction, priorities), and come up with a vision of 'health' that is reasonable for them and a set of sustainable lifestyle choices they can make to reach and maintain that goal.
What does all this ultimately mean? Well, from my point of view it means I'm likely to keep eating cookies for breakfast, and work to resolve any discontent with the life and the body that choice creates.