Simple Diet For Weight Loss

Is there such a thing as ‘Starvation effect’ that prevents Weight Loss when dieting?
I’ve been successfully losing weight for about the last five to six months (about 3 and a half stones so far), but recently the loss has begun to plateau, and it’s making me kind of cranky. I started at 20st5, and I’m aiming for around 15st. I’m eating a varied diet of around 1200-1400 calories a day, and doing an hour of heart-rate monitored aerobic exercise 4-5 times a week at the Gym (Bike and treadmill: the machines say I’m burning approx 800 calories per session). My job is extremely sedentary. Some friends have mentioned a ‘Starvation effect’ where I might be consuming *too little* and my Metabolism is slowing down to compensate. I thought weight loss was a simple matter of ‘Energy in, Energy out’. Is it possible that I am eating too little or doing too much exercise? Stepping on the scales each week and only seeing a 1lb loss (if anything) is a little disheartening, but I know I’ve got further to go.
1lb is good at this point. Thats what you should be losing- but I would vary the exercise more.
Easy Detox & Cleansing Tips For Health, Diet & Weight Loss Dr. Katerina Sheffield