Whose fault is obesity? Most of the blame rests with one culprit.

There’s a scene in the 2002 movie “Real Women Have Curves” where the heroine, Ana (America Ferrera), who struggles with her weight, is in a restaurant with her mother, Carmen (Lupe Ontiveros). Dessert comes, and Carmen looks daggers at Ana, whom she habitually belittles and criticizes about, among other things, her body.

“Don’t eat the flan,” Carmen says.

Ana takes a defiant bite and pushes it away.

Carmen represents an entire school of thought on obesity. “Just eat less” is the school’s line. “It’s a matter of individual responsibility.”

If you’re of the Don’t-Eat-the-Flan school, can we try a little hypothetical?

Let’s say I’m organizing a tennis tournament at your local club. You’re pretty good, but you’re still surprised when you see the pairings and find that, in the first round, you’re playing Serena Williams.

You lose, because, of course, you lose.

Whose fault is it? Yours, because your forehand really needs work? Or mine, because I put you in a situation where you were tragically, comically overmatched?

Mine, of course. And this is exactly what has happened with food. A combination of factors created a Serena Williams of a food environment, and most of us don’t have the forehand for it. Making matters worse, we have people pushing ineffective solutions that leave eaters confused and disempowered. For most of us, no tennis lesson (read: diet) on the planet will make us Serena-ready.

Some 73 percent of Americans are overweight or obese. When three-quarters of humans can’t navigate the system successfully, the problem is the system, not the humans. So let’s look at the system and give credit — er, blame — where it’s due.

The lion’s share - I’ll go with 61 percent (and, yes, of course I’m totally making this up to give some sense of how I think responsibility gets divvied up) - goes to the food industry, which developed product after product that was deliberately designed to be overeaten.

Food manufacturers didn’t start off trying to make people fat and sick. They just wanted to sell more food; that’s their job. But as they got better at it, it became clear that weight gain was a byproduct of that business model. Now, the people who run those companies are caught between their fiduciary responsibility to maximize shareholder value and their social responsibility to not contribute to a large and growing public health problem.

Fiduciary seems to win out, particularly since the food industry doesn’t just put the food out there, manufacturers also commission research and fund lobbying arms to make sure consumers are given every reason to eat more of their product. Marion Nestle’s books “Food Politics” and “Unsavory Truth” detail how the industry has influenced the government-issued Dietary Guidelines and the body of evidence on the health effects of foods.

Those manufacturers also get a meaningful assist from just about everyone in the retail environment, who make sure engineered deliciousness is in your face 24/7. No matter what’s in the rest of your store, there’s Snickers at the checkout.

Manufacturers aren’t the only ones trying to sell us deliciousness, of course. That’s an important goal of food, isn’t it? Restaurants fight for stomach share, too, and one of the weapons they have is portion size. You’ve probably seen the data, and the illustrations where modern-day portions dwarf portions of yore. Soda comes in sizes that top a half-gallon. Muffins are as big as softballs. Fast-food burgers are three times the size they were in the 1950s.

The fact that there’s more food on every plate wouldn’t matter if we didn’t eat it. But we do. The more there is, the more we eat. If you increase portion size by 50 percent, we’ll eat 10 to 40 percent more. Double it, and we’ll increase consumption 30 to 55 percent.

I’ll give restaurants a 5 percent slice of the blame pie.

Once our weight started to creep up, we got a burgeoning sector of people telling us how to lose it. Many of them are well-intentioned, genuinely wanting to help people who struggle with their weight. Others are out-and-out grifters. Since we can’t get inside the heads of diet purveyors, it’s hard to know which is which, but I can’t wrap my mind around the idea that anybody really believes your blood type matters for weight loss. On the other hand, I think a lot of, say, the low-carb folks are operating in good faith.

Nevertheless, the net result is that the American eating public has internalized the idea that weight loss is more about what you eat than how much you eat, and if only you find the right combination of foods, or macronutrients, you’ll be fine. Sometimes, that helps people - cutting out carbs can make eating less easier - but most of those efforts fail, and leave people feeling as though they have failed. Diets are a very serious net negative, and I’ll give diet purveyors 9 percent of the blame.

Diet doctors have gotten help, though. Nutrition scientists, mostly sober, public-health-minded academics, nevertheless have fueled some important misconceptions about diet and health. I’ve been doing this long enough to remember when lots of research pointed to the problem with dietary fat. Then came sugar, and carbohydrates in general. Now it’s ultra-processed foods, and precision nutrition is coming up fast. None of these is out-and-out wrong! And I think they’re onto something with the ultra-processed foods, but the message has not been anything close to consistent. Can you blame people for throwing up their hands and heading for the drive-through? If scientists can’t make sense of diet, what hope is there for the rest of us? Let’s say 4 percent for scientists.

Of course, they would work in total obscurity if it weren’t for the media. Including me. Before I came around to the enlightened, clearly correct view I now hold, I wrote a whole book about eating less fat. It was wrong! (Although it was also funny.) In my defense, lots of media is worse than me, and collectively we play a big role in dietary confusion. Media gets 7 percent.

I’m not absolving us, the eaters. Yes, the world is stacked against us, but our collective susceptibility to dumb diets and quick fixes doesn’t redound to our credit. (Although I’m not overweight now, I was for a long time, so I’ve earned the royal “we.”) At the end of the day, we didn’t just eat the flan, we made every event - classes, meetings, ballgames, car rides - a flan-eating opportunity. So we get 10 percent.

There are, of course, other factors, so I’ll leave the remaining 4 percent for stuff I didn’t mention but that you’re going to tell me I overlooked.

Assigning blame isn’t just spleen-venting (that’s merely an ancillary benefit). Figuring out the root cause of obesity is Step One to fixing the problem. But the fixes that have been floated to change our food environment - taxes, bans, labeling, education - are both unlikely to pass in our political environment and unlikely to make a dent in the problem; none have led to significant population-level weight loss anywhere they’ve been tried.

Which brings us to the new weight-loss drugs. I am optimistic that the safety will pan out, and they will eventually become affordable and accessible for all who want them.

An objection I’m hearing to these drugs is that they don’t tackle the root cause of obesity, but I think that’s exactly what they do. We’ve been undone by industrial-strength temptation, and the new meds confer industrial-strength resistance. They make us Serena-ready.

If you want to change our flan-everywhere environment, tackle the demand, not the supply.

Tamar Haspel is the author of “To Boldly Grow: Finding Joy, Adventure, and Dinner in Your Own Backyard.” An oyster farmer on Cape Cod, she writes Unearthed, a monthly commentary in pursuit of a more constructive conversation on divisive food-policy issues.