Don't worry about self flagellating christian guilt mania diet nonsense. Think about how much you eat. Think about the effect of being even 1 potato chip per plate out between energy demands and consumption. Daily energy demands for a woman approximates 10 mega joules. Pure fat has an energy density of around 3000 Kj/100g. So your energy demands can be met each day by a little over 333 gms of fat. A finger of butter or 3-5 chocolate bars. If you're 1/20th out, that's 17 gms of fat per day. Or 7.3Kg/year of pure fat. But adipose tissue is a complex of fat cells storing around 15Mj/Kg. So this translates to a 12.3Kg/year weight gain or loss (loss is easier to model as an extreme, due to fat cells having basel energy requirements). To the naive this would suggest a forward path of extreme conscious dietry control, but a little reflection will demonstrate that since most people are in equilibrium subconscious mechanisms must already tightly control body composition.
For what follows it is important to understand what you are. You are not your appetite. Now if we examine you closely, we see, merci, there is no clear place where you end and the rest of the universe begins. Likewise, there is no place where I end and the rest of the universe begins. Now invoking transitivity we see there is there is no place where you end and I begin. We are one. But you and I are words people use frequently and take pains not to confuse. This difference in language suggests a difference in reality that yields predictive power when dichotomised into two words. There's no place where red ends and green begins either, but red is not green even if they are on a spectrum. Rhetoricians call red=green argument from false spectrum. But just like I am not you, your breath is not you, your finger is not you, your eyes are not you, your thyroid, pituitary gland and medulla are not you, no neuron is you, infact, none of the parts of you are you.
You don't exist as discrete thing, because as we have now established, not only is there no place where you end, there is not even a place where you begin. But we know the word is useful! So what can we say? Since you are reading these words you are the ensemble of strongly connected (i.e primarily brain) causality interactions connected to the input of these words. In the same way the word Paris is has greater predictive power the closer it is to the epicenter of connectivity of the French capital, but Paris is not the geographical or connective epicentre of Paris. Now France is to Paris, as your brain is to the language processing areas of your brain. But within France there are other cities such as Le Mon Atier- les-Bains or Grenoble, that should not be called Paris because their connectivity with Paris is very weak. So to, within your brain there are subsystems the language processing areas are not meaning fully connected to. They operate independently. Many of parts of the cortex and brain stem are ancient and do not differ appreciably to identical subsystems in rats, crocodiles, or even lobsters. In particular those parts of the brain that regulate basic needs such as arousal, temperature, blood pressure, and appetite are very ancient.
We already established that you and these other sub regions of the brain must be different if the word you is to retain meaning. Hence we come to the following remarkable conclusion. You share your body with a lobster! This lobster, or perhaps more romantically, "inner rat", is a simple creature, and it controls homeostasis. It controls appetite and activity and You have no direct control over it. All you can do is move it from place to place and buy different things for it to eat. Otherwise you have less control over it than it has over you because it is able to influence your feelings of reward, temperature, hunger and activity.
This creature is very good at measuring your body composition and controlling your appetite without conscious control. It's a lovely, sophisticated device. If you don't want to get fat, eat cashews, not marshmellows, even though the former have four times the energy density, for they are a source of plant life to be and due to the common ancestory of man and plant a good source of life for women; a rich bounty that tells the lobster its food supply is plentiful. Marshmellows and other refined foods she may need to eat a mountain of to get, say, her folic acid needs met; a poor diet which may activate biological strategies for dealing with food scarcity (Store emergency reserves; We can't live on this stuff!).
Lack of exercise does not make people fat through decreased energy demands. Rather it changes the lobsters's perception as to how much weight the body may carry without detrimental effect. Exercised induced overheating and over energy expenditure from lugging extra weight around (it takes twice as much energy to lift twice as much weight) will be measured by the brain through metabolic products in the blood, activating body composition modification via change of appetite and activity levels, moving body composition to a form better suited to the exercise rich environment in which it finds itself. Everyone knows muscle fibres grow in response to exercise, but adaptions take place throughout the body and brain to minimise exercise induced stress and maximise efficiency. It's an optimisation problem with two variables. Reserves vs. movement efficiency. The global optima depends on the weightings of these two variables. You can change the weighting through conscious behavior, behavior which subconscious brain regions will then measure to control your appetite. God, who lets no good deed go unpunished, has ensured the traditional energy reduction diet has the effect of activating genetic food scarcity strategies, increasing appetite, decreasing activity and so resulting in subsequent weight gain.
My advise to anyone who wants to loose weight; deny yourself no complex food that primitive man would eat (vegetables, red meat, including organs, fish, eggs, fruit, nuts, all simply prepared). Your lobster knows how to be respond to those foods. Eat slowly so appetite change can control intake. Within this structure eat whatever tastes the most appealing. Foods which have something you lack will taste nicer till the need is for filled. Exercise to create weight induced over heating and carry stress to activate weight reduction strategies. How many overweight long distance runners do you know?