According to recent studies, approximately 40% of American adults are obese with that number approaching 47% for Hispanic and African Americans. Even for those people who are not classified as "obese," losing weight is a common goal. So, it is not surprising that dieting and weight loss is a $66 billion industry in the US.
Unfortunately, while every year millions of Americans will try various diets or weight loss programs, most will not succeed in the long term. Over the years, many will become stuck in the cycle of weight loss and gain known as "yo-yo dieting." There are important scientific reasons why fad diets and rapid weight loss does not work in the long run. I would like to examine the three main reasons why diets don't work.
Reason 1: Deprivation of Macronutrients
Most fad diets or weight loss programs that promise rapid weight loss rely on the reduction of one of the three macronutrients: fat, protein, or carbohydrates. Over the past decade or two, "low-carb" diets such as Atkins or Keto diet have gained popularity. In the 1960s, fat was vilified as the cause of obesity and chronic disease lading to many low-fat or fat-free diets. Fortunately, there are very few diets that want to restrict protein, as the limiting of protein could be very dangerous.
The problem with long term restriction of any of the macronutrients is that you are using willpower to overcome the body's natural desire for a balance of protein, fat, and carbs. If you deprive yourself of carbs long enough, you will crave carbs more and more. If you keep yourself from having any fat, you will end up craving fats. Rather than depriving yourself of a particular macronutrient, I would suggest improving the quality instead. Rather than having two slices of white bread, try having some brown rice. Instead of using vegetable oils or margarine, try using coconut or olive oil. Avocadoes also provide a healthy fat.
Reason 2: Leptin
Basically, leptin is the hormone that tells your brain and your body that you have had enough to eat, so you feel full and do not want to eat anymore. We also have known for some time that when you lose weight rapidly, your body will suppress the production of leptin as part of the starvation response. This is a survival mechanism designed to get you to eat more calories to replace the weight that you are losing when you are "starving."
Now, when you lose weight rapidly, the body goes into starvation mode and suppresses leptin production. As you begin to gain weight back, your body will typically resume normal production of leptin. However, there are indications that when you gain and lose weight repeatedly (yo-yo dieting) or lose a really large amount of weight rapidly, leptin production can remain lo or suppressed, even when you are gaining weight.
Reason 3: Persistent Metabolic Adaptation
When I was in college, I lived close to my aunt. One day, she found a stray cat on her doorstep emaciated and near death from starvation. She decided to take the cat in and the cat survived under her care. Six months later, the cat went from being a walking skeleton to a rather chubby cat. A year later, the cat was obese and I used to joke that it looked like it ate a watermelon. That cat would be obese for the rest of its life. Why? Persistent metabolic adaptation. When your body thinks it is starving, it slows down your metabolism to conserve energy, sometimes permanently.
Since scientists cannot starve people and then study them, research on this has been sparse. In 2016, however, a study was conducted on 14 former contestants of the TV show The Biggest Loser. They found 13 of the 14 had gained back a significant amount of the weight and 4 out of 14 actually now weighted more than their original starting weight (gained back more than they lost). In their study, researchers found that the common denominator was lower metabolism for the former contestants. Even the one contestant that had kept the weight off had a lower metabolism. Interestingly, this lower metabolism persisted even six years after the initial weight loss.
New York Times discussion of the study. Business Insider discussion of the study.
As with leptin resistance discussed above, metabolic adaptation is a survival mechanism from the feast or famine days from which we evolved. When you lose weight rapidly by severely restricting calories or macronutrients, you body "thinks" you are starving to death and survival mechanisms kick in. Even if you are obese and have plenty of fat reserves, if you lose weight too fast,your body goes into starvation mode and it lowers your metabolism to try to conserve calories and keep you alive. When this state persists for weeks instead of a few days, your body makes a permanent adaptation. Your body "assumes" that you are not in a condition where you can reliably provide enough calories, so it stays in starvation mode permanently in an effort to keep you alive in what it perceives as a persistent famine state.
Thus, you body is 1) lowering your metabolism, and 2) sending out signals saying "whenever you get a chance to eat, consume as many calories as possible." You can see how this makes it nearly impossible to be successful long term. This method relies completely on willpower and there are very few people who can maintain that level of willpower, going against their own biology, for the remainder of their lives.
A Better Way
If dieting does not work, then what does? My recommendation is lifestyle change, combined with gradual weight loss. While it may not be as flashy or grab headlines in the tabloids, eating a healthy, balanced diet with proper food portions, will help you lose weight sustainably and permanently. The first step that I would take is replacement rather than deprivation. Rather than saying, "I am not going to eat any sweets for dessert," say, "I am going to have a piece of fresh fruit for dessert." If you can make this a habit, in a few weeks, you won't miss the cake or ice cram any more and will welcome the sweetness of an apple or pear. In addition, whenever possible, replace processed or pre-packaged foods with natural foods. For example, have some natural dark chocolate instead of an oreo cookie.
If you are struggling with weight loss, I would be happy to put together a plan of action for you to achieve your goals once and for all. You can sign up for a free strategy session and together we can take the first step to weight loss mastery.