Refined carbs have been processed more, and the natural fiber has been removed or changed, so they have a bigger and quicker impact on your metabolism and blood sugar. Eating refined carbohydrates spikes your blood sugar, spurs food cravings, and has been linked to several health conditions, including type 2 diabetes and obesity.   
Sugar alcohols are also classified as carbohydrates, but they don’t typically spike your blood sugar in the same way as sugar, which is why they’re usually allowed on keto diets. You subtract the fiber and sugar alcohols from the total carb count of a meal to find out your net carb count.
Since fiber doesn’t get broken down by the body, it is different than other carbs and doesn’t spike your blood sugar. Instead, it feeds the healthy bacteria (probiotics) in your gut. The bacteria in your gut can use the fiber to produce beneficial fatty acids. For this reason, the fiber content of foods does not count toward your carb limit.
What Are Calories?
Almost every food has calories, even foods with little to no carbohydrates. Calories are measurable units of energy you obtain from your food or drink. You can find calorie counts on food items. Various apps, trackers, and wearables allow you to monitor how many calories you’re burning with certain activities and how many calories you’re taking in when you eat.
Processed and sugary foods tend to have more calories than natural healthy whole foods. However, some low-calorie foods like diet soda can be problematic for your metabolism, not provide any nutritional value, and impede your weight loss goals. Just because a food is high-calorie doesn’t mean it’s unhealthy, and vice versa. For example, a can of full-fat coconut milk provides nutritional value and around 700 calories, but it could certainly fit into a healthy diet for some people, particularly those consuming more healthy fats on a ketogenic diet. Olive oil provides 119 calories per tablespoon, and one avocado provides 322 calories. Healthy fats tend to have a high calorie count.
How many calories you require to function each day depends on several factors, such as your:
- Activity level
- Weight loss goals
Each of the three primary macronutrients in your diet contains calories:
- Carbohydrates: 4 calories per gram
- Fat: 9 calories per gram
- Protein: 4 calories per gram
Fiber may differ in calorie content depending on if it’s insoluble or soluble fiber.
The Dietary Guidelines for Americans recommend men intake around 2,000 to 3,000 calories daily, and women should intake around 1,600 to 2,000 calories daily. People who are more active may require more calories. Other factors affect caloric requirements, such as pregnancy, breastfeeding, and illness.  
Empty-calorie foods have little to no nutritional value and are usually high in sugar and refined carbs. Alcoholic drinks are considered empty calories.
Counting Calories for Weight Loss