Mid-January is the time many Americans are well along into their New Year's Resolution to lose weight.

While it's great to swap healthy foods for unhealthy snacks and meals, there are some healthy - but sneaky - saboteurs to your new regime.

Sometimes the healthy foods you swap for the old ones are high in fat and calories, according to a report in Health.com. So remember to watch the serving size - even with fruits, nuts, yogurt and salads.

Here is a list of some healthy foods but worst calorie culprits - so watch the portions.

Avocado
The avocado is loaded with nutrients, fiber and monounsaturated fats, but it is also high in fat. A good serving size is about one-fifth of an avocado and is around 50 calories. A whole avocado is about 350 calories. So watch the guacamole appetizer.

Red wine
While red wine has been proven to reduce risk for heart disease, cancers and Alzheimer's disease, it should be taken in moderation. There are about 130 calories in a 5-ounce glass of wine.

Nuts
Nuts have omega-3 fatty acids, protein, vitamin E and fiber but they have a lot of calories. One-quarter of a cup of almonds has 132 calories and if you're not paying attention, you can eat them by the cupful.

Trail mix
Dried fruits, nuts and oats can pack a caloric punch to your diet. Many of the store-bought brands of trail mix use honey, sugar and chocolate. Proceed with caution.

Dried fruit
While dried fruits are merely normal fruits that have had the water removed, beware of that lack of volume. Calories are concentrated. A cup of dried fruit has five to eight times more calories and sugar that a cup of fresh fruit.

Chocolate
Dark chocolate is healthy, but that's not an excuse to go overboard. Dark chocolate has disease-battling polyphenols and has been associated with weight loss, but only in small doses. One ounce of dark chocolate has 155 calories and nine grams of fat; five of those are saturated.