While some foods are considered healthy and nourishing, they might not always be optimal for weight loss.

Registered dietitian nutritionist Ilana Muhlstein spoke with Fox News Digital in an interview about certain foods that could stunt health and fitness goals.

"There’s definitely a big difference between healthy and healthy for weight loss," the Los Angeles-based expert said. "This is something that I see so many people struggle with."

LEAN, MEAN PROTEIN: HOW MUCH SHOULD YOU BE EATING? NUTRITIONIST REVEALS ANSWERS

It's possible to eat healthy foods yet still pack on pounds, she noted, "which is not healthy for your overall body, especially if you have weight to lose."

Here are six surprising foods that might not help you lose weight.

While granola is a classic topping for healthy snacks like yogurt and smoothie bowls, Muhlstein likened it to a "crushed-up cookie."

"People look at it as super healthy, but those oats are usually being tossed with nut butters, oils, maple syrup, honey, thrown-in chocolate chips and coconut shavings," she said. "They’re baked, it’s dense and a cup of granola can be 600 calories."

2 SURPRISING FOODS FOR FALL THAT ARE DELICIOUS, HEALTHY AND EASY TO PREPARE

Even a sprinkle of granola can add up to 200 calories, according to Muhlstein.

"[It's] really not a great bang for your buck when you’re talking about filling up on foods and staying within a healthy calorie range for weight loss," she said.

While oat-based foods like overnight oats and oatmeal can work well for people who are athletic, they might not be the best choice for those on weight-loss journeys, Muhlstein said.

"It kind of sits with them … they’re not able to burn it off so quickly," she said. "It’s really good before a workout, as you’re taking those carbs and using them efficiently."

DRINKING SOY MILK COULD REDUCE RISK FACTORS FOR HEART DISEASE, RESEARCH SHOWS

Muhlstein recommends pairing oat recipes with yogurt or protein powder for a more optimal meal.

Nut butters are "not a protein source," even though whole nuts contain protein, the nutritionist stated.

They can be used to add flavor or healthy fat to recipes like salad dressing, stir-fry or smoothies, she said.

"If you are trying to eat peanut butter for protein and you’re having a peanut butter and jelly sandwich, you are having a lot of calories, a lot of carbs … and very, very little protein overall," Muhlstein noted.

Seed-based snacks like chia seed puddings have grown in popularity as a healthy breakfast option.

Chia seed puddings, however, can be made with sweeteners like honey, maple syrup and coconut milk, which make them "very high in calories" and low in protein, Muhlstein revealed.

"It has plenty of good, healthy fats and could be great for your digestion, [with] Omega-3s and fiber," she said.

"But overall, it's not the slimmest choice if you’re trying to drop pounds on the scale and maintain a leaner frame."

While avocado is well-known for being a healthy fat, eating too much can hamper weight-loss goals. 

Most women only need about one avocado’s worth of fat in a whole day, according to Muhlstein.

DIET CRISIS IN AMERICA: CELEBRITY FITNESS TRAINER AND MOM TOUTS ‘NO RULES’ NUTRITION PLAN

"When you get a salad with half an avocado on top of the dressing, on top of the nuts and everything else, it’s probably a lot," she said. "I usually recommend about a quarter to a third of an avocado at a time."

During the COVID-19 pandemic lockdowns, many people turned to baking sourdough bread, which spiked its popularity.

For more Health articles, visit www.foxnews/health

While sourdough does have some healthy qualities, as it’s fermented and can have a lower glycemic index, Muhlstein pointed out that it "still has calories."

"It’s still not cauliflower," she said. "It’s really funny how many people almost treat it like it is."

Some of Muhlstein's clients have made a habit of baking a loaf of sourdough every week and then eating the whole thing, she said.

"It’s really not working for their weight loss," she said. "But it’s the last thing they think is the problem, because it’s been touted as such a health food."

Pesto can be a delicious condiment on salads, vegetables and other dishes, but it is usually made with "lots of olive oil, lots of Parmesan cheese and lots of pine nuts," Muhlstein cautioned.

CLICK HERE TO SIGN UP FOR OUR HEALTH NEWSLETTER

"When you have that dipped with your bread, and it becomes excessive, it is a very high-calorie condiment," she said.

The nutritionist recommends thinning out a pesto recipe with lemon juice, Greek yogurt, or nutritional yeast instead of cheese and nuts.

Adding more basil will help thicken the recipe, while more water will help blend it.

"I know that sounds sacrilege to some chefs, but if you are really trying to get the flavor, there are ways to make a leaner pesto," Muhlstein added.