In an effort to lose body fat, you are probably doing all that you can to ensure that the scale reads a few pounds less each week. This weight loss should be FAT, not muscle or water. To guarantee the loss is pure body fat, you need to implement a solid weight lifting program at least twice per week and maintain proper hydration.
The body loves to burn dormant muscle tissue for fuel instead of first tapping into stored body fat. Carrying more muscle enables your body to burn more calories at rest, thus making your metabolism more efficient. The body does not like this as it prefers to store fat for "survival" reasons and not lug around too much muscle. You on the other hand probably have other ideas!
Another issue is dehydration. Our bodies are roughly 60% water and even a 2% level of dehydration will cause your body to work harder than usual. This work puts undue stress on your heart and other organs and can cause high blood pressure, fatigue, migraines and joint stiffness amongst other issues. Make sure you get AT LEAST the recommended 8-10 glasses of water per day- if you are active, you need at about 3-4 liters every single day. There is some controversy about water consumption, but if you are a bodybuilder or competitive athlete who trains 5-6 days per week- you need more water than the average person. Ingesting more protein in an effort to build muscle stresses the liver and kidneys and they need to be flushed to avoid toxicity issues in the body.
Along with a healthy diet, a consistent cardio schedule that meets your unique needs and a few days of weight lifting and you will be able to build muscle and step on the scale at the end of the week knowing the numbers are down because you have in fact burned body fat!