Diet and obesity

Average per capita energy consumption of the world from 1961 to 2002

The dietary energy supply is the food available for human consumption, usually expressed in kilocalories per person per day. It gives an overestimate of the total amount of food consumed as it reflects both food consumed and food wasted. The per capita dietary energy supply varies markedly between different regions and countries. It has also changed significantly over time.[2] From the early 1970s to the late 1990s, the average calories available per person per day (the amount of food bought) has increased in all part of the world except Eastern Europe and parts of Africa. The United States had the highest availability with 3654 kilo calories per person in 1996.[3] This increased further in 2002 to 3770.[4] During the late 1990s, Europeans had 3394 kilo calories per person, in the developing areas of Asia there were 2648 kilo calories per person, and in sub-Sahara Africa people had 2176 kilo calories per person.[3][5]

Change over time of the macronutrient composition of the US male diet.

Change over time of the macronutrient composition of the US female diet.

USDA chart showing the increase in soda consumption and the decrease in milk consumption from 1947 to 2001.[6]

From 1971 – 2000, the average daily number of calories which women consumed in the United States increased by 335 calories per day (1542 calories in 1971 and 1877 calories in 2000). For men, the average increase was 168 calories per day (2450 calories in 1971 and 2618 calories in 2000). Most of these extra calories came from an increase in carbohydrate consumption, though there was also an increase in fat consumption over the same time period.[7] The increase in caloric consumption is attributed primarily to the "consumption of food away from home; increased energy consumption from salty snacks, soft drinks, and pizza; and increased portion sizes".[7] Other sources note that the consumption of soft drinks and other sweetened beverages now accounts for almost 25 percent of daily calories in young adults in America.[8] As these estimates are based on a person's recall, they may underestimate the amount of calories actually consumed.[7]

As societies become increasingly reliant on energy-dense fast-food meals, the association between fast food consumption and obesity becomes more concerning.[9] In the United States consumption of fast food meals has tripled and calorie intake from fast food has quadrupled between 1977 and 1995.[10] Consumption of sweetened drinks is also believed to be a major contributor to the rising rates of obesity.[11]

A comparison of a typical cheeseburger 20 years ago (left) which had 333 calories with a modern cheeseburger (right) which contains 590 calories as per the National Heart, Lung, and Blood Institute

The portion size of many prepackage and restaurant foods has increased in both the United States and Denmark since the 1970s.[7] Fast food servings, for example, are 2 to 5 times larger than they were in the 1980s. Evidence has shown that larger portions of energy-dense foods lead to greater energy intake and thus to greater rates of obesity.[12][13]

A 2010 study published in the American Journal of Clinical Nutrition closely tracked 373,803 people over a period of 8 years across 10 countries. At its conclusion, the study reported that meat consumption is positively associated with weight gain in men and women.[14] In response, the National Cattlemen's Beef Association countered that increased meat consumption may not be associated with fat gain.[15] However, a subsequent response controlled for just abdominal fat across a sample of 91,214 people found that even when controlling for calories and lifestyle factors, meat consumption is linked with obesity.[16] Further population studies, reviews, and meta-analysis studies have corroborated the claim that greater meat consumption is linked to greater rates of obesity.[17][18]

Excessive intake of sugar-sweetened beverages (including fruit juices, soft drinks, fruit drinks, sports drinks, energy and vitamin water drinks, sweetened iced tea, and lemonade) increases the risk of metabolic syndrome – which includes obesity and type 2 diabetes among its pathologies – in adults and children by adding to overall energy intake.[19][20][21][22] Children who excessively consume sugar in foods and beverages have a high risk of becoming overweight.[21][22] Reviews indicate that governmental health policies should be implemented to discourage intake of sugar-sweetened beverages and reduce the 21st century trends of increased prevalence of obesity in children and adults.[19][20][21][22] Other than adding excessive calories, the mechanisms by which high sugar consumption causes obesity are unclear because of limitations in clinical research involving uncontrolled factors, such as overall diet, physical activity, and sedentary lifestyle.[19][20][23]

New agricultural technologies have led to an overall reduction in the cost of food relative to household income, especially in high-income countries. In his popular book, "The Omnivore's Dilemma," the journalist Michael Pollan linked the subsidies offered to farmers of corn, soy, wheat, and rice through the U.S. farm bill to over-consumption of calories derived from these crops and to rising obesity rates.[24] While increased consumption of foods derived from these commodities is correlated with an increase in BMI (at the population level), no current research supports a causal relationship between farm subsidies and obesity.[25] From a policy perspective, the cost of sugar would actually decrease in the US if the commodity support programs in the farm bill were removed, largely due to the tariffs in the farm bill that restrict the importation of lower-cost sugar available on the global market.[26]

Participation by adults in the United States Department of Agriculture Supplemental Nutrition Assistance Program (i.e. Food Stamps) is positively associated with obesity, waist circumference, elevated fasting glucose, and metabolic syndrome.[27]

Evidence does not support the commonly expressed view that some obese people eat little yet gain weight due to a slow metabolism. On average obese people have a greater energy expenditure than normal weight or thin people and actually have higher BMRs.[28][29] This is because it takes more energy to maintain an increased body mass.[30] Obese people also underreport how much food they consume compared to those of normal weight.[31] Tests of human subjects carried out in a calorimeter support this conclusion.[32]

• List of countries by dietary calorie intake
• Criticism of fast food