A Chef Turned Nutritionist Explains Why How You Cook Matters More Than What You Eat

Most of us have spent years obsessing over the right foods to eat. We track macros, swap ingredients, follow meal plans. But according to culinary nutrition expert Maryna Rubel, we've been asking the wrong question.

"The biggest gap in how people approach healthy eating isn't in the grocery store," says Rubel. "It's in the kitchen – in the thirty minutes between buying the right ingredients and putting them on the plate."

Rubel spent years working in professional restaurant kitchens across England before nutrition science changed how she read everything she already knew about cooking. In October 2023, she completed her certification as a Specialist in Healthy Nutrition and Nutritionology through the IPHM (International Practitioners of Holistic Medicine).

"Working in professional kitchens, you develop a very precise relationship with ingredients," she explains. "You know exactly what heat does to a protein, what fat does to flavor. When I started studying nutrition, I realized those same decisions - temperature, technique, timing - also determine what the body actually gets from that food."

After years in the UK and Belgium, Rubel relocated to the United States in 2024, with a combination rarely seen in the wellness industry: a trained cook who can explain the biochemistry of what happens to food once it's eaten.

Every diet book, every wellness account, every nutritionist tells you what to put on your plate. Leafy greens, lean proteins, complex carbohydrates – the list is familiar. What almost none of them cover is that cooking method changes the nutritional profile of that food significantly.

"Broccoli is a good example," Rubel says. "It contains a compound called sulforaphane, which has real anti-inflammatory properties. But boiling broccoli for more than a few minutes destroys most of it, depending on how long and how hot. Steaming lightly or eating it slightly raw preserves it. Same vegetable. Very different outcome for the body."

Overcooked eggs are significantly harder for the body to use. Garlic crushed and left to rest for ten minutes before cooking activates compounds that are lost when it goes straight into heat. Cooling cooked rice or potatoes before eating them increases their resistant starch content, meaning a slower glucose release – changing the glycemic impact of the same meal.

"None of this is particularly complicated once you know it - but most people never come across it in one place," she says. "It sits in the gap between cooking education and nutrition education. I've lived on both sides of that gap, which is why I can work in it."

Rubel's approach is built around a few habits that don't require changing what you eat – only how you prepare it.

Heat management is the first principle. Different nutrients have different heat tolerances. Water-soluble vitamins like C and B vitamins are fragile; fat-soluble ones like A, D, E, and K need fat present to be absorbed at all. Cooking spinach briefly in a small amount of olive oil makes its nutrients more available to the body than eating it raw.

The temperature you start with matters as much as the temperature you cook at. Tomatoes are a useful example: lycopene, their main antioxidant, actually becomes more bioavailable when tomatoes are cooked – but only when there's fat in the pan. A raw tomato salad with no oil delivers less of it than a sauce simmered slowly in olive oil. The ingredient hasn't changed. The preparation has turned it into a different nutritional experience entirely.

"It's not a perfect science," Rubel acknowledges. "Cooking times vary, ingredients vary, people vary. But the direction is consistent - and in most home cooking situations, these shifts are significant enough to matter."

Sequencing matters too – both within a meal and within the cooking process. Adding garlic to cold oil and bringing it up to heat together is fundamentally different from adding it to a hot pan. The flavor is different. So is the chemistry.

And timing, often overlooked, can shift a food's metabolic effect considerably. Cooked and cooled starches form resistant starch. Resistant starch feeds gut bacteria and slows glucose absorption. A bowl of pasta eaten hot is a different metabolic event than the same pasta eaten as a cold salad the next day.

"This is what I mean when I say cooking is a nutritional decision," Rubel says. "Every technique you use in the kitchen – how long, how hot, in what order – is either working for you or against you. Most people don't know which one they're doing, because no one ever told them the two were connected."

What most wellness experts can't offer, Rubel can: she's worked both sides – the professional kitchen and the science of what happens to food once it's eaten. Most nutritionists advise on food selection. Most chefs focus on technique and flavor. She works in the space between them – and that, she says, is where most of the results actually are.

"I'm not telling people to overhaul their diet," she says. "I'm showing them that the food they already eat can work much harder for them if they understand what's happening in the pan."

If you've been eating well for years and still feel like something isn't working – that's likely where the answer has been the whole time.