Scientists act on the basis of existing paradigms (ie, theoretical frameworks) that describe what is to be observed, the questions that are supposed to be asked, and how the results of scientific investigations should be interpreted.1 But, when demographic trends foster public health concerns, as obesity and type 2 diabetes are doing today, some researchers view existing paradigms as incomplete or ineffective and explore alternatives to long-standing assumptions (ie, paradigm shifts; see Kuhn1). The lectures in this supplement to Nutrition Today represent a number of emerging paradigms, from diverse areas such as metabolism, weight gain, human behavior, public health, disease risk, cognition, and human performance (Figure). All provide evaluations of the benefits of water consumption, and a few compare water to sugar-containing beverages.
Some of the most important scientific discoveries and inventions have been greeted by the general public with nonchalance because their qualities and applications appear to be obvious and natural. Water consumption is a fine example. Most adults readily acknowledge the value of water consumption, yet when asked to justify this opinion, they can provide little or no scientific or clinical evidence. The following points provide summaries of such evidence, which appear in the preceding articles.
* Sugar-containing beverages may encourage fat deposition and weight gain, because they have a high glycemic index and suppress fat metabolism. Water does not stimulate insulin and thus does not influence metabolism in the same way.
* Epidemiological statistics show that the rising incidence of obesity and type 2 diabetes in Mexico and other countries parallels the increase of carbonated soft-drink consumption.
* Unlike competitive endurance athletes who exercise for more than 1 hour per day, recreational enthusiasts do not need to consume carbohydrates (ie, in solid food or beverages) before, during, or after exercise. If they do this, the added calories counteract one of the benefits of exercise: reducing or maintaining body weight.
* French adults, who habitually consumed little water each day, increased their water intake (ie, week 1, 247 mL/d; week 5, >900 mL) after receiving simple instructions.
* Thirst is not perceived until a body mass loss of −1% to −2% exists; thus, adults need to drink even when they are not thirsty. This is true because, when thirst is initially perceived, urine is concentrated almost maximally.
* The kidney is capable of regulating a fluid excess more effectively than a fluid deficit.
These conference presentations also present future directions for research, in a variety of content areas. Although experimental evidence supports the following concepts, additional studies are needed to clarify, confirm, or refute present-day paradigms.
* Which hydration markers validly identify mild dehydration and require little or no technical expertise or expense?
* Are the dynamics of water turnover in obese individuals different from adults with a normal body mass index?
* What dimensions of mood (ie, vigor, fatigue, tension) and cognition (ie, short-term memory, pattern recognition, vigilance) are most sensitive to mild dehydration?
* What simple techniques encourage optimal daily water intake by adults and children?
* What are the influences of water consumption on satiety, food item choices, and weight management?
* What are the subtle effects of long-term mild dehydration on health?
* In which diseases are incidence and risk reduced by increasing daily water consumption?
* Do sex differences exist for the above questions?
Further, the Hydration for Health Conference generated concepts that have interesting implications for public health policies and government action.
* Nutritional survey data, in combination with research findings, were converted into recommendations for healthy beverage choices and governmental action in Mexico.
* When adults are given instructions to drink more water during daily activities, they increase their water intake.
* Adults who have a great risk of kidney stone formation (lithiasis) reduce their risk by increasing water intake.
* Dehydration impairs cognitive performance and mood in a dose-dependent manner, beginning at a body mass loss of −1% to −2%. This level of dehydration occurs in many occupations.
* Consuming water and reducing the intake of sugar-containing beverages may help children and adolescents avoid excess energy intake and avoid weight gain, plus increase fat metabolism. To avoid obesity, it is important to intervene at an early age.
In particular, the preliminary evidence regarding the positive role of water intake in the reduced theoretical risk of obesity and type 2 diabetes should be confirmed or refuted by longitudinal studies. Countries can no longer ignore the rising health care costs associated with these conditions. By 2030, annual health care costs attributable to obesity and overweight in the United States are projected to be $860 to $956 billion; this would account for $1 in every $6 spent on health care.2 Similarly, rising health care costs for diabetes treatment in the United States will approach $200 billion per year by the year 2012.3
Finally, Hydration for Health Conference speakers recommended approaches to altering unwanted public health trends, by improving personal nutrition. These include (a) changes in nutrition education and governmental dietary guidelines, (b) action by grassroots consumer groups that influence the ingredients contained in popular commercial products,4 and (c) government incentives that encourage manufacturers to produce healthier foods and beverages. Because these efforts rely on research, it will be interesting to see how scientific paradigms shift during the coming decade, in response to investigations that focus on the role of water consumption in healthy personal hydration practices.