You are hungry because of the increased metabolic demands of resistance training. You are breaking down muscles in the gym, depleting them of sugar, or glycogen, and burning calories. Resistance training can burn many calories, and the increases in caloric demand do not stop when you leave the gym. A good weight training session can raise your basal metabolic rate, according to research at Colorado State University.
One of the things that occurs when you train is that amino acids are broken down or utilized by the body for various tasks. Research at the University of Western Ontario has shown that active people may require more protein than their less-active counterparts. Good sources of protein include lean cuts of beef, chicken, fish and lean cuts of pork. Milk is an excellent source of protein and can easily be consumed for extra calories in between meals. For those practicing any type of vegetarian lifestyle, various soy products are available.
Carbohydrates are the preferred fuel for your body, as they are the easiest to burn. One of the primary sources of energy when lifting is your muscles' supply of glycogen, or sugar. If you burn it all up, you need to "top off your tank" for optimal performance next time. While it is possible to take in minimal carbohydrates and still perform, if you are constantly hungry, you might wish to examine this aspect of your diet. In addition, research at Texas A&M has shown that combining protein with carbohydrates can significantly enhance your recovery.
Yes, some fat is essential. Omega-3 and omega-6 fatty acids are required for a variety of functions within the body, including hormonal regulation. Lifting is a strain on your endocrine, or hormonal system. If you are not getting essential fatty acids in your diet, you can consume extra fish oils for omega-3 fatty acids, such as salmon, and use flaxseed when cooking for omega-6. Diets too low in fat can have a negative impact on your ability to recover. Research at Helsinki University has shown that diets too low in fat lower your testosterone levels, which will negatively impact your ability to recover.
Putting It All Together
When you eat is almost as important as what you eat. If you are always hungry, ensure that you are properly fueled prior to a training session. A modest amount of protein and simple carbohydrates pre-workout can provide you with extra energy and leave you feeling less fatigued. After the workout, ensure that you are getting protein and carbohydrates together as discussed above. Divide your meals into smaller portions, and eat them over the course of the day. If you are still hungry, drink milk in between meals, a good source of protein, carbohydrates and small amounts of fat. Train hard, and eat well.