Portion size matters. As most of us know from experience, it matters for your waistline because consuming more energy than you exert tips the bathroom scales in a direction you probably don’t like. But it also matters from a sustainability point of view because eating more food than your body needs wastes both food and the natural resources required to produce it.

This may not be the message you want to hear at the tail end of Thanksgiving weekend, seeing as the average American consumes 4,500 calories on Turkey Day alone, according to the Calorie Control Council, the marketing board for the diet food industry. That same group says that the average American eats 3,600 calories on an ordinary day. Since the USDA says that an average active human needs only 2,700 calories a day, we are, on average, over-eating by 900 calories per day.

According to Sustainable America, a nonprofit organization that looks to make the nation’s food and fuel systems more efficient, in the United States it takes roughly 10 units of fossil fuel energy to produce one unit of food energy. So if you are eating 900 food energy units more than your body requires to function, you are also consuming 9,000 more fossil fuel energy units than you ought to be.

The GRACE Communications Foundation, a nonprofit organization dedicated to creating a more sustainable food system, created a water footprint calculator to help illustrate how everyday actions – from washing dishes to watering the lawn to buying groceries – affect water use. Users can calculate how their type of diet (vegan, vegetarian, and omnivore) affects water usage. According to their calculations, the food the average meat-eating American eats takes 1,395 gallons of water day to produce, the food for the average vegetarian 690 gallons/day and the food for the average vegan 638 gallons/day. If average Americans stuck to USDA calorie guidelines, we could collectively reduce water usage by as much as a third.

Yes, as any dieter knows a person looking to eat less could whittle away at his calorie count by vowing not to eat in between meals. But we also need to take a hard look at mealtime portion sizes. Even before studies showed how fast food meal portions have increased by 300 percent since 1950, there were anthropological studies that analyzed the size of the Last Supper as presented in 52 paintings created between 1000 and 1900. One of those studies indicates portion size has been increasing in a linear fashion for at least a millennium.

But some evidence also indicates that smaller portions could be normalized over time. A study led by Eric Robinson Institute of Psychology, Health, and Society at the University of Liverpool in England tested whether reducing a food portion size “renormalizes” perceptions of what constitutes a normal amount of that food to eat and results in people selecting and consuming smaller portions of that food in the future. The findings, published last April in the American Journal of Clinical Nutrition, suggest hope both for our waistlines and for a more sustainable food systems.

“Because consumer preferences appear to be driven by environmental influences, reducing food portion sizes may recalibrate perceptions of what constitutes a ‘normal’ amount of food to eat and, in doing so, decrease how much consumers choose to eat,” Robinson wrote.

While the USDA My Plate visual suggests that a meal contain specific weights and measures of all five basic food groups (vegetables, fruits, grains, protein, and dairy), author and sustainable eating advocate Michael Pollan offers portioning advice that doesn’t involve pulling out a kitchen scale: “Eat real food, not too much, mostly plants.”

CHRISTINE BURNS RUDALEVIGE is a food writer, recipe developer and tester and cooking teacher in Brunswick, and the author of “Green Plate Special,” a cookbook from Islandport based on these columns. She can be contacted at [email protected].

paSTA with Brussels Sprouts and Chorizo Cream

This recipe was developed by food writer and blogger Andie Mitchell and is published in her “Eating in the Middle” cookbook, a non-diet book that aims to redefine what a balanced diet means. Each serving has about 450 calories, but satisfies like many more.

Serves 4

4 cups trimmed and quartered Brussels sprouts

2 teaspoons extra-virgin olive oil

1/2 teaspoon salt

1/2 cup finely chopped chorizo (or pancetta)

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1/2 pound whole-wheat rotini

2 medium leeks, white and light green parts only, thinly sliced (about 11/2 cups)

¼ teaspoon freshly ground black pepper

3 garlic cloves, minced

½ cup half-and-half

¼ cup low-sodium chicken broth

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¼ cup grated Parmesan cheese

Preheat the oven to 425 degrees F.

Toss the Brussels sprouts and olive oil on a large rimmed baking sheet. Spread in a single layer, cut sides down, and season with ¼ teaspoon of the salt. Roast until browned and tender, 30 to 35 minutes. Set aside.

In a 12-inch nonstick skillet set over medium-high heat, cook the chorizo until browned and crispy, 6 to 8 minutes. Transfer to a small bowl. Return the skillet to the stovetop.

Meanwhile, cook the pasta according to the package directions. Drain.

To the drippings in the chorizo skillet, add the leeks, the remaining ¼ teaspoon salt, and the pepper. Cook, stirring frequently, until the leeks begin to soften, 2 to 3 minutes. Add the garlic and cook, stirring constantly, until fragrant, about 30 seconds. Reduce the heat to low, add the half-and-half and chicken broth, and cook for 2 minutes. Add the drained rotini, crispy chorizo, and roasted Brussels sprouts, and toss to coat in the sauce. Stir in the Parmesan cheese.

Divide the pasta among 4 plates and serve immediately.