Obesity refers to the accumulation of excess body fat, leading to a condition of excess body mass, increased risk of disease and decreased life expectancy. It is also defined in terms of body mass index (BMI) or body weight per square meter height; a BMI>30 kg/m^2 is a sign of obesity.
One of the main causes of obesity is poor nutritional choices, including sweetened beverages (constitute 25% of daily energy needs in US), chips and 'fast food'. As per the statistics, the obesity rate in the US increased from 14.5% (1970) to 30.9% (2000); and this increase is directly correlated with an average increase in the amount of energy consumed per capita. The increasing obesity is connected to increased consumption of energy-dense fast-foods, including soft drinks, iced teas, fruit drinks, snacks, chips, etc. A chief reason of this shift towards fast/processed food is the agricultural policy which has caused processed food to be cheaper than fruits and vegetables.
Obesity can be treated by making lifestyle changes, including higher intakes of dietary fiber (through fruits and vegetables) and decreased consumption of energy-dense foods.
The most prominent effect of nutrition on obesity is the value-sizing of less nutritional food as seen in the United States. In many European countries, meals are divided into different segments, which includes many different side dishes and main dishes so that many nutrients can be ingested by the body. However, in the United States, a meal usually only consists of a certain type of food that is not as nutritional as compared to eating, say salad and a plate of pasta. These foods include hamburgers, hot dogs, and what not. Furthermore, in the United States, there is a tendency to make everything 'a meal' with adding more non-nutritious food like french fries and chicken tenders. This just causes people to eat a meal just full of less nutritional food, which can lead to obesity.
Poor nutrition and lack of physical activity go hand in hand with causing obesity. Lack of quality, nutritious food can lead to an increase in sugar and fat consumption. Eating a well balanced diet of proteins, fats, and carbohydrates will give you the energy you need for your daily functioning. Food is your body's fuel. It's like gas to a car, if you put low quality fuel in a Lamborghini it will not run efficiently. Your body works the same way. Quality food and nutrition will allow your body to perform at it's best and help you avoid obesity.
Poor nutrition and obesity don't always go hand in hand, but more often than not someone who is obese is eating an unhealthy diet. This unhealthy diet can cause malnutrition. There are people who are obese who exercise regularly and eat healthy food, but for those who do not it can be very detrimental.
Poor nutrition comes from diet. For example, if someone is obese because they consume too many calories each day, causing weight gain, and their diet is rich in sugary drinks, fast food, and doesn't contain a lot of whole grains, fruits and vegetables, they will become nutrient deficient. When nutrition is poor it can cause many problems. There may be an excess amount of proteins and dairy being consumed which has been shown to cause a higher likelihood of cancer. The body may not be able to heal itself as quickly when it succumbs to an injury. The immune system can weaken and then someone may not overcome an illness as quickly either. These are some of the effects of (poor) nutrition in an obese person.