In a nutshell, WeightWatchers is so bad because it is a calorie controlled diet. Granted - it uses a points system to restrict your calorie intake, but at the end of the day it encourages you to follow the 'Eat less - Do more' way of thinking.
Since this way of thinking has been introduced; obesity has skyrocketed and this is due to the following reason:
When you restrict your calorie intake, firstly your body sends you a signal - hunger. This causes you to crave food which leads to overeating. If you ignore this signal, your body goes into 'starvation mode' and thus hangs on to any fat that it can and lean tissue is 'burnt as fuel'.
There was an experiment done in America in May 1944 - The Minnesota Starvation Experiment.
36 men - aged 20-33 were chosen (for their physical and mental resilience) from 200 volunteers.
The experiment lasted a year and was split into 4 phases:
Phase 1 - The Control Period.
This phase lasted 12 weeks and the intention of it was to determine the calorie requirements of the men. It was found that the men needed 3210 calories per day in order to maintain their weight whilst walking 22 miles per week (Just over 3 miles per day)
Phase 2 - The Starvation Period.
This phase lasted 24 weeks and was, in effect, a calorie controlled diet of approx. 1600 calories per day. The diet was comprised of foods that were generally available in Europe during this time period.
Phase 3 - Restricted Rehab Period.
This phase lasted 12 weeks and in it, the men were split into four groups and were given different calorie, protein and vitamin levels to see which would nourish them back to health
Phase 4 - Unrestricted Rehab Period.
This last phase lasted 8 weeks and the men were allowed to eat whatever they liked. The research team carefully monitored what they ate.
The men all reported massive hunger, weakness and exhaustion.
They lost 21% of their strength in the first 12 weeks of the starvation period.
They experienced muscle wasting and dizziness.
They became obsessed with food.
They had to team up with another member of the experiment to avoid 'cheating' (eating more than allowed).
The government is keen to impress upon us that if we create a calorie deficit of 3500 per week we WILL lose 1 lb of fat
Do not aim to lose weight too quickly, or you could end up losing muscle rather than fat. Aim for half to 1 kg (1-2 lbs) per week. This means eating 500-1,000 fewer calories than you were eating and drinking before. You should lose 6-12 kg if you keep this up for three months. from hereand
A pedometer gives the user the ability to measure how much they have done and a goal to aspire to. Walking the recommended 10,000 steps in a day will burn 500 calories, and doing that five days a week will burn 3,500 calories – enough to lose 500g (1lb) of body fat from hereand
Aim to lose about 0.5-1kg (1-2lb) a week until you reach a healthy weight for your height. You should be able to lose this amount if you eat about 500 to 600 calories fewer a day than you need. from here
The Minnesota Experiment renders this advice to be utter rubbish:
The calorie deficit in the starvation phase was 1630 calories per day by eating less and almost 3000 calories per week by doing more! The average weight loss of the men was 37 lbs (1.5 lbs per week). If this formula was correct, every man should have lost 95 lbs in fat during the 24 weeks. (The lightest man in the study would have ended up at under 3 stone!)
During the experiment it was determined that some men needed to be restricted to 1000 calories per day in order to attain the desired weight loss and if the 3500 calorie deficit myth is to be believed then these men should have lost over 5 lbs per week or 120 lbs over the course of the 24 weeks. What actually happened was that the human body adjusted it's energy requirement to combat any further weight loss.
All men reached a plateau at around week 20 and one man even recorded a weight gain during the final 4 weeks! but this was attributed to him chewing gum - His results were not used.
During the final phase - the unrestricted phase, all of the men overate and binged in order to regain their calorie deficit. One of the men - Harold Blickenstaff, was sick on the bus on the way back from one of the meals on phase 4; he found that he simply
Couldn't satisfy [his] craving for food by filling up [his] stomachMany also reported eating excessively after they left Minnesota; Jasper Garner described it as a 'year long cavity' that needed to be filled.
Many like Roscoe Hinkle put on substantial weight after the experiment had concluded.
This is why WeightWatchers will not work in the long term you would need to restrict your calorie intake for life; even then your body would reduce the amount of calories it needed to maintain its weight and thus you would need to reduce your calorie intake even more just to maintain weight.