Fat has more than twice the calories per gram as protein or carbohydrates, so one way to cut calories is to limit the amount of fat you consume. Although reducing fat consumption can be a good strategy, it's possible to get too little fat. Some types of fats are essential, so it's better to limit unhealthy saturated fat while still getting sufficient amounts of the healthier unsaturated fats.
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Recommended Fat Intake
Adults should get between 20 and 35 percent of their calories from fat, 10 and 35 percent of calories from protein, and 45 to 65 percent of calories from carbohydrates. The essential omega-6 unsaturated fats, which come from nuts and seeds as well as many vegetable oils, should comprise between 5 and 10 percent of your calories, and the essential omega-3 fats found in fatty fish and flaxseeds, should make up between 0.6 and 1.2 percent of your calories. In a 2,000-calorie diet, that translates to 11 to 22 grams of omega-6 fatty acids and 1.3 to 2.6 grams of omega-3 fats. The rest of the fat you consume can be a mix of the healthy monounsaturated fats, found in olive oil, nuts and avocados, and the saturated fats from meat, poultry and dairy products, but preferably mostly monounsaturated fats.
Fat and Vitamin Deficiencies
Certain vitamins can only be absorbed in the presence of fat, including vitamins A, D, E and K. If you don't get enough fat in your diet, you may develop deficiencies of these essential vitamins. A deficiency of vitamin A can cause rough skin and night blindness and make it harder for your body to fight off infections. Vitamin D deficiency may cause weak bones and muscles and increase your risk for high blood pressure, cancer and infectious diseases. If you don't get enough vitamin K, your blood may not clot properly. Vitamin E deficiencies are rare but can cause vision problems, abnormal eye movements, weak muscles, loss of muscle mass, unsteady walking, and kidney and liver problems.
Essential Fatty Acid Deficiency
An essential fatty acid deficiency can cause your skin to become dry and scaly, impair wound healing and make you more likely to develop infections. If no omega-3 or omega-6 fats are consumed, this condition can develop in as little as one week. Even if enough omega-6 fats are taken in, inadequate omega-3 fats can cause deficiency symptoms such as difficulties with memory and learning. The good news is, most people eat enough fat to prevent a deficiency.
Other Potential Issues From Too Little Fat
A diet that is too low in fat can also cause a number of other symptoms, such as anemia, loss of menstrual periods, decreased thyroid function, bone loss, low energy levels, infections of the gums and other dental health problems, and infertility. If you get fewer than 20 percent of your calories from fat, you're more likely to get hungry sooner after eating, as fat slows down the emptying of your stomach so you feel full longer. Getting less than 25 percent of your calories from fat may even make binge eating more likely, according to registered dietitian Joanne Larsen. If your very-low-fat diet also consists of less than 1,200 calories per day, it can slow your metabolism, which makes it more likely that you'll regain any weight you lose in the form of fat once you start eating a more regular diet.