Based on current trends, unless there are major changes in our eating habits and level of physical activities, half of the adults in the United States will be obese by the year 2030. If you are currently overweight, the probability is extremely high that in time you will become obese -- where overweight is defined as a body mass index, BMI, over 25 and obese as over 30. If a child is overweight, the probability that child will be obese as an adult is close to 100 percent.
The endless advertisements, television commercials and self-help diet books are evidence of the absence of an easy fix. The problem is already contributing significantly to the increasing incidence and costs associated with diabetes, cardiovascular disease, stroke, and osteoarthritis.
If anyone had a cure for this problem, the vast diet industry would go the way of buggy whip manufacturing. It turns out the common weight-loss wisdom of reducing intake by about 500 calories a day will result in slow and steady weight loss of about a pound per week is flawed. That rule doesn't take into account the way the body adapts to changes in diet. As anyone who has lost weight will tell you, as their weight went down, if they wanted to maintain their reduced weight or lose more, they had to consume still fewer calories. If you are accustomed to taking in 2,000 calories a day and after losing weight need only 1,750 to maintain your lower weight, you will feel hungry; if you take in 2,000, you won't feel hungry but you will re-accumulate the weight you worked so hard to lose.
Taking a realistic period of time for weight loss into account, it appears that for an average overweight adult a reduction in caloric intake of about 15 calories a day will lead to an eventual body weight change of about two pounds -- with half of the weight change being achieved in about one year, while 95 percent of the weight loss will take about three years. Like so many fundamental characteristics of biological systems, genuine weight loss is a slow orderly process.
Although we don't understand all the underlying mechanisms, most diets have reduced effects over time because the body adjusts to them. This has been shown to be true for Slim Fast, NutriSystem, Weight Watchers, the Atkins diet, the grapefruit diet, and even the water diet. The exception to this rule seems to be a diet based on portion control. Although there are no controlled trials of the strategy of limiting portion size, it appears that those who select this route for weight control decrease the size of their portions as they lose weight.
The principles of weight loss seem to be deceptively simple. If you take in more calories than you burn, you will inevitably gain weight -- take in less and lose weight. However there are some interesting nuances to this equation. To burn some calories requires more energy output than others. It turns out the number of calories burned given the same activity is also variable -- not only from one person to another but even in the same person at different times. If you have a very efficient metabolism, you will burn fewer calories for a given level of activity and the efficiency of metabolism varies within the same person. To complicate matters further, it appears that metabolic efficiency increases with increasing age. This helps explain why as we age we need fewer calories for weight maintenance. If as you age you maintain a constant caloric intake, you will gain weight even if you maintain the same level of activity. There are many other complex interactions that contribute to the increasing prevalence of obesity and its associated maladies.
Although not based on a controlled trial, it seems the best investment for anyone trying to control their weight is a good scale. It turns out those who simply weigh themselves every day when they get up in the morning, control their weight better than any other group. Whether the object is weight maintenance or loss, this seems to reenforce their goal and results in their adjusting food intake and their level of physical activity.