All the calories in your diet come from one of four sources: carbohydrate, fat, protein and alcohol. Alcohol doesn't figure into any calculations of the best nutrient ratios for weight loss. Experts continue to debate the optimal ratio of the three main nutrient sources for weight loss. Traditional diets ask you to eat about two-thirds carbs with limited fat and protein, and low-carb diets allow higher proportions of fat and protein with fewer carbs. What's more important than the precise ratio of macronutrients is burning more calories than you eat.
Carbs supply your body with four calories per gram and generally come from plant sources. Minimally processed carbohydrates like blueberries, salad greens, beans and oatmeal also give you ample fiber to make you feel full and help your digestive system function properly. Carbohydrates provide glucose, the body's preferred fuel.
Protein also provides four calories per gram, but it can come from both plant and animal sources. Protein is important for proper cellular function.
Fat provides nine calories per gram, which is why you are often advised to avoid it when trying to lose weight.
The nutrient ratio that is most often cited by government, health and fitness professionals is 55 to 60 percent of calories from carbohydrate, no more than 30 percent from fat and the remaining 10 to 15 percent from protein.
Low-carb diet plans such as Atkins argue that Americans eat way too many carbohydrates, and recommend that the bulk of your calories come from fat and protein, and less than 10 percent come from carbohydrate in the beginning phases.
Over the past several decades, many studies have analyzed the effectiveness of a variety of nutrient ratios for both short- and long-term weight loss, and the answers are still unclear. A 2003 study in the "Journal of Nutrition" showed that reducing carbohydrate levels helped women lose weight and improve body composition. Other studies show similar benefits on low-fat, high-carb diets.
A 2009 study published in "The New England Journal of Medicine" compared a variety of different nutrient ratio plans and found that they all produced about the same results after two years.
Weight loss depends on eating fewer calories than you use in a day. In fact, a Kansas State University professor of human nutrition experimented on himself with an all-junk-food diet: the professor successfully lost more than 25 pounds in 10 weeks by eating less than 1,800 calories a day, even if it was mostly fat and sugar.
The key point for weight loss is that you can choose the nutrient ratio that works best for you. If you crave carbs, then enjoy a bowl of oatmeal. If you can't live without steak, then eat it. Just keep your total intake below what you're able to burn in a day.