体重管理

栄養は健康的な体重を維持するための重要な要素である。

体重管理とは、健康的な体重を達成・維持するための行動や技術、生理学的プロセスを指す。ほとんどの体重管理技術は、健康的な食事と毎日の身体活動を促進する長期的なライフスタイル戦略を包含している。さらに、体重管理には、長期にわたって体重を追跡し、個人によって異なる理想的な体重を特定する有意義な方法を開発することが含まれる。

体重管理戦略では、多くの場合、ゆっくりではあるが着実に体重を減らして健康的な体重を達成し、その後理想体重を維持することに焦点が当てられている。しかし、健康に対する体重にとらわれないアプローチもまた、健康上の好ましい結果をもたらすことが示されている。

肥満は、2型糖尿病、高血圧、心血管疾患など、多くの慢性疾患発症の危険因子であるため、体重管理の基礎科学と、健康的な体重を獲得・維持するための戦略を理解することは非常に重要である。

主な要因

人の体重には、食事、身体活動、遺伝、環境要因、医療支援、医薬品、病気など、多くの要因がある。これらの要因はそれぞれ異なる方法で、程度の差こそあれ体重に影響を及ぼすが、意識的な行動修正によって影響を及ぼすことができるため、医療専門家は食事と身体活動の重要性を最もよく強調する。健康的な体重を得るには、分量の調節、自己管理、毎日の食事の一貫性など、一般的なテクニックを認識することが必要である。健康的な体重に到達した後は、この安定した体重を維持するために、さらに身体活動や個人の環境や食事パターンのコントロールが必要となる。さらに、長期的な体重管理には、プライマリ・ケアの医学的監督と長期的なフォローアップという形での医療支援が有用であることが示されている。

以下は、ヒトにおける体重管理の主要な構成要素についてのレビューである。

エネルギーバランス

体重管理の背後にある科学は複雑であるが、体重管理を支配する重要な概念の1つはエネルギーバランスである。エネルギーバランスとは、ある人が消費したカロリー数と、同じ人が一定期間に消費した（消費した）カロリー数との差を表す言葉である。エネルギー収支方程式に関しては、3つのシナリオが考えられる：

• 摂取カロリー（食べ物、飲み物）＝ 消費カロリー（基礎代謝量、身体活動、食べ物の熱発生効果、急性疾患）
  • 結果： 体重は変化しない
• 消費カロリー＞消費カロリー
  • 正のエネルギー収支としても知られる。
  • 結果：体重は増加する： 体重が増加する
• 消費カロリー＜消費カロリー
  • 負のエネルギーバランスとしても知られている。
  • 結果：体重が減少する： 体重が減少する

人が消費するカロリーは、食べ物や飲み物の摂取によるものである。人が消費するカロリーは、基礎代謝量と日々の身体活動から得られる。人体は、特に果物、野菜、肉類で構成された食事を摂ることで、一定の時間内に消費カロリーが消費カロリーを大幅に上回ったり、逆に消費カロリーが消費カロリーを大幅に上回ったりしないように、中立的なエネルギーバランスを保つことに長けている。このエネルギーバランスは、食欲を抑制または刺激するレプチン（抑制）、グレリン（刺激）、コレシストキニン（抑制）などのホルモンによって調節されている。

カロリー量を含む栄養表示情報を示す画像

食事療法

個人が摂取する飲食物の量は、その人が摂取する飲食物の種類と同様に、体重管理に関与する可能性がある。例えば、ソーダやジュースのような甘味飲料の摂取は、エネルギー摂取量の増加につながるが、付随する食品摂取量の減少では中和されない。分量の増加もエネルギー摂取量の増加につながる。

身体活動

トレッドミルでのランニングは、自宅やジムでできる身体活動のひとつだ。

身体活動は、その人の職業活動に関連したもの、ウォーキングやサイクリングのような仕事に関連しない日常的なもの、あるいはレクリエーションやチームスポーツのような活動の形態もある。 具体的な活動の種類は、子ども、妊婦、高齢者などの集団に合わせることができる。自分のフィットネス・レベルに合わせた活動は、身体が適切に回復するのを促し、運動による怪我を予防する。

運動不足はエネルギー消費量の低下につながり、子どもから大人まで肥満率に影響を与える要因となっている。運動不足は心臓病のリスクも高めるため、運動不足は世界的な問題となっている。定期的な身体活動は、糖尿病、心臓病、脂質異常症（高コレステロール）などの非伝染性疾患のリスクを減らすことができる。

Basal metabolic rate

Basal metabolic rate (BMR) is one of the main components of a person's daily energy expenditure. It is defined as the amount of energy that is expended during a given amount of time by a person at rest. This energy at rest is used to pump blood throughout the body, maintain proper brain function, break down toxins, and ensure other bodily functions. Technically speaking, BMR is the energy the body expends during the following specific conditions: immediately after waking up, while in a resting state, and after fasting for 12–14 hours. Sometimes the term Resting Metabolic (RMR) is used in place of BMR, but RMR is not solely measured under the previously listed stringent conditions and it is about 10% more than BMR.

The BMR is directly proportional to a person's lean body mass. In other words, the more lean body mass a person has, the higher their BMR. BMR is also affected by acute illnesses and increases with burns, fractures, infections, fevers, etc. It can be measured via direct and indirect calorimetry. However, it is also possible to approximately estimate BMR using several equations that factor in a person's age, sex, height, and weight. Some of the most popular and accurate equations used to calculate BMR are the original Harris-Benedict equations, the revised Harris-Benedict equations, and the Mifflin St. Jeor equation.

The original Harris-Benedict Equations are as follows:

• BMR (Males) in Kcals/day = 66.47 + 13.75 (weight in kg) + 5.0 (height in cm) - 6.76 (age in years)
• BMR (Females) in Kcals/day = 655.1 + 9.56 (weight in kg) + 1.85 (height in cm) – 4.68 (age in years)

The revised Harris-Benedict Equations are as follows:

• BMR (Males) in Kcals/day = 88.36 + 13.40 (weight in kg) + 4.8 (height in cm) – 5.68 (age in years)
• BMR (Females) in Kcals/day = 447.59 + 9.25 (weight in kg) + 3.10 (height in cm) – 4.33 (age in years)

The Mifflin St. Jeor Equation is as follows:

• BMR (Males) in Kcals/day = 9.99 (weight in kg) + 6.25 (height in cm) – 4.92 (age in years) + 5
• BMR (Females) in Kcals/day = 9.99 (weight in kg) + 6.25 (height in cm) – 4.92 (age in years) – 161

The Mifflin St. Jeor Equation has been found to be the most accurate predictor of BMR compared to BMR measured by direct and indirect calorimetry.

Body mass index

Main article: Body mass index

Body mass index (BMI) is a value used to get a general sense of a person's overall mass and is calculated using a person's height and weight. It is more often used than weight alone to determine if an individual is underweight, normal weight, overweight, or obese. The following two equations can used to calculate BMI depending on the units used for height (meters vs. inches) and weight (kilograms vs. pounds):

$\mathrm{B}\mathrm{M}\mathrm{I}=\frac{{\text{weight}}_{\text{kg}}}{{{\text{height}}_{\text{m}}}^2}$

or

$\mathrm{B}\mathrm{M}\mathrm{I}=\frac{{\text{weight}}_{\text{lbs}}}{{{\text{height}}_{\text{in}}}^2}\times 703$

Though BMI is often used to help assess for excess weight, it is not a perfect representation of a person's body fat percentage. For example, an individual can have a higher than normal BMI but a normal body fat percentage if they have higher than average muscle mass. This is because excess muscle contributes to a higher weight. Since BMI is not a perfect representation of a person's body fat percentage, other measurements like waist circumference are often used to better assess for unhealthy excess weight.

The following table shows how different ranges of BMIs are often categorized into underweight, normal weight, overweight, and obese:

Waist circumference may be used as an alternative method to assess weight.

Classification of Overweight and Obesity by Body Mass Index (BMI)

Category	BMI
Underweight	< 18.5
Normal Weight	18.5 – 24.9
Overweight	25.0 – 29.9
Obesity (Class I)	30.0 – 34.9
Obesity (Class II)	35.0 – 39.9
Obesity (Class III)	≥ 40.0

On average, groups of people with "obese" BMIs may have a higher risk of developing illnesses like diabetes, hypertension, dyslipidemia (high cholesterol), liver disease, and some cancers. "Underweight" BMIs may indicate malnutrition or other health problems. However, BMI has limitations when used to describe individual health rather than describing populations of people.

Complicating factors

Thermogenic effect of food

The thermogenic effect of food is another component of a person's daily energy expenditure and refers to the amount of energy it takes the body to digest, absorb, and metabolize nutrients in the diet. The amount of energy expended while processing food differs by individual but on average it amounts to about 10% the number of calories consumed during a given time period. Processing proteins and carbohydrates has more of a thermogenic effect than does processing fats.

Medications

Certain medications can cause either weight loss or weight gain. Such side effects are often listed for each medication and should be considered when attempting to manage a person's weight.

Metanalysis has shown that phentermine and topiramate, pramlintide, naltrexone, bupropion, and liraglutide have been shown to induce weight loss. Semaglutide is another anti-obesity drug that is also used for blood sugar control.

Diseases

Medical conditions associated with weight gain include hypothyroidism, Cushing's syndrome, Polycystic Ovary Syndrome (PCOS), and congestive heart failure. Medical conditions such as cancer, gastrointestinal illness, psychiatric disorders, infections, endocrine disorders, and neurologic disorders may lead to weight loss.

Commonly associated with weight gain

Polycystic ovary syndrome (PCOS), which is characterized by insulin resistance and hyperandrogenism, is a common condition that has been linked to obesity. A combination of genetics, lifestyle, and environment appear to contribute to the hormonal changes responsible for weight gain and obesity seen in individuals with PCOS. There appears to be a bidirectional relationship between obesity and PCOS, whereby PCOS increases the risk of obesity and similarly, obesity has been found to exacerbate PCOS hormonal differences and clinical symptoms. Obesity has been linked with pancreatic β-cell dysfunction and insulin resistance. In diabetes, impaired β-islet cells are responsible for the lack of blood glucose control. Individuals with a higher body mass index concerning for obesity may have increased levels of hormones, proinflammatory markers, and glycerol, which can contribute to insulin resistance. The combined effects of impaired pancreatic β-islet cells and insulin resistance increase the likelihood of developing diabetes.

In individuals with blood sugar levels in the prediabetic range, weight loss was demonstrated to have many benefits including improved glycemic control and a reduced risk of developing type 2 diabetes.

Commonly associated with weight loss

Common gastrointestinal disorders associated with weight loss are malabsorption due to Celiac disease or chronic pancreatitis. Depression and eating disorders such as anorexia nervosa can also contribute to weight loss. Infectious causes of weight loss include HIV/AIDS.

While Type 1 diabetes has been found to cause weight loss, type 2 diabetes has been associated with weight gain. Other endocrine causes of weight loss include hyperthyroidism and chronic adrenal insufficiency.

Intentional weight loss

Diets

See also: List of diets

As weight loss depends partly on calorie intake, different kinds of calorie-reduced diets, such as those emphasizing particular macronutrients (low-fat, low-carbohydrate, etc.), have been shown to be equally effective as weight loss tools. Nonetheless, a low-saturated fat diet complemented with high fiber can be helpful for those who are found to be obese based on BMI. Furthermore, a low-carbohydrate diet can have the added benefits of blood sugar control in those with Type 2 Diabetes Mellitus. A low-carbohydrate diet can also improve weight loss, HDL, and cholesterol in certain individuals. Compared to a typical diet, low-carbohydrate, low-fat, and moderate macronutrient diets can all positively impact weight loss. However, weight regain is common, and the outcome of a diet can vary widely depending on the individual. Rather than focusing on the nuances of each diet type, molding one diet in a way that the person can continuously adhere in the long-term could be beneficial for weight loss.

DASH diet

The Dietary Approaches to Stop Hypertension (DASH) diet focuses on increasing the consumption of fruits, vegetables, whole grains and low-fat dairy products. DASH offers an intervention to manage elevated blood pressures and prevent cardiovascular disease non-pharmacologically. In addition, combining the DASH diet with a reduced sodium intake will further decrease blood pressure, but is not required for therapeutic effect. This is because it has been proven to be effective at a wide range of sodium intake levels. More recent reviews of DASH have continued to advocate its efficacy as an affordable weight loss tool, but stress that diet adherence is key to produce the desired results.

Fruits and vegetables are considered staples of the Mediterranean diet.

Mediterranean diet

The Mediterranean diet involves eating fruits, vegetables, whole grains and beans while replacing butter with extra-virgin olive oil and limiting red meats, dairy, sweets, and processed foods. It has been shown to be effective for long term weight loss with added cardiovascular health benefits. For example, the Mediterranean diet can lead to decreased triglyceride and lipid levels as well as improved blood pressure readings. It can also improve blood sugar levels in those diagnosed with Type 2 Diabetes Mellitus.

Ketogenic diet

The ketogenic or "keto" diet involves intake of less than 50 g of carbohydrates daily along with increased fat and protein amounts. One type of ketogenic or low carbohydrate diet is the "Atkins" Diet, which does not restrict protein and fat amounts. However, there are other ketogenic diets that place restrictions on the total amount of daily proteins and fats.

Plant-based diet

The plant-based diet is largely based on consumption of beans, grains, fruits, and vegetables and removal of meat, fish, and occasionally dairy and egg products from intake. In other words, fiber and unsaturated fat intake is increased and consumption of higher calorie meats and saturated fats is decreased. This diet has been shown to reduce BMI and introduce positive body composition changes when compared to a carnivore diet.

Intermittent fasting

Intermittent fasting (IF) involves consistent fasting blocks of time where fewer or no calories are consumed. Intermittent fasting has been shown to improve fasting blood glucose levels and insulin resistance with a concurrent reduction in BMI.

Strategies

An dinner example of portion sizes relative to food groups

Modifying plate size

Some studies have suggested that using smaller plates might help people to consume smaller portion sizes.

Modifying portion sizes may impact energy intake. Those who are presented with larger portion sizes do not report to have high levels of satiety. In other words, hunger and satiety signals could be ignored with large portion sizes. In a study focused on portion sizes, participants consumed 31% less calories with the small portion sized of a 6-inch submarine sandwich compared with the large portion size of a 12-inch submarine sandwich. Increased portions have occurred simultaneously with the increase in obesity rates. Large portion sizes could be one of the factors contributing to the current increase in average body weight in the US. Evidence from a systematic review of 72 randomized controlled trials indicates that people consistently eat more food when offered larger portion, package, or tableware sizes as opposed to smaller size alternatives.

Choosing low-calorie foods

The majority of guidelines agree that a calorie deficit, particularly 500-750 kcal daily, can be recommended to those who want to lose weight. A moderate decrease in caloric intake will lead to a slow weight loss, which is often more beneficial than a rapid weight loss for long term weight management. For example, low fat meats reduce the total amount of calories and cholesterol consumed.

Increasing protein intake

A high protein diet relative to a low-fat or high-carbohydrate diet may increase thermogenesis and decrease appetite leading to weight reduction, particularly 3-6 months into a diet when rapid weight loss is observed. However, these advantages may be reduced later at 12–24 months into a diet during the slow weight loss phase.

Eating more soup

Studies have demonstrated that when compared to solid foods, soup ingestion decreases the amount of energy intake and increases feelings of satiety. When soup is consumed before a meal, there is a 20% decrease in the number of calories consumed during said meal.

Eating more dairy

Milk intake has been advocated as a weight loss strategy due to its calcium and other nutrients.

Studies have shown that a diet high in dairy decreases total body fat. This occurs because a high amount of dietary calcium increases the amount of energy and fat excreted from the body. Other studies have noted that dairy sources of calcium lead to greater weight loss than supplemental calcium intake. This could be due to the bioactive components of dairy sources, especially when combined with a lower calorie diet. Since most natural dairy products contain fat content, there is a common understanding that this may cause weight gain. However, dairy contains ingredients such as whey protein and certain combinations of protein/calcium nutrients that induce a positive effect on satiety, increase energy loss, and assists weight loss.

Eating more vegetables

Fruits and vegetables have been shown to increase satiety and decrease hunger signals. These food groups have a low energy density, mainly due to the high water content and partly due to the fiber content. The reduction of energy density has been shown to enhance satiety. The water content adds satisfying weight without excess calories and fiber slows gastric emptying. Studies have also shown that fiber decreases hunger and also decreases total energy intake.

Increasing fiber intake

Fruits and vegetables are two sources of fiber as discussed above. Dietary fiber has been suggested to aid weight management by inducing satiety, decreasing absorption of macronutrients and promoting secretion of gut hormones. Dietary fiber consists of non-digestible carbohydrates and lignin, which are a structural component in plants.

Fruits and vegetables contain fiber which has been shown to improve satiety and help with weight loss.

Due to the high volume or water content of fiber-rich foods, fiber displaces available calories and nutrients from the diet. Consumption of viscous fibers delays gastric emptying, which may cause an extended feeling of fullness. Satiety is also induced by increasing chewing, which limits food intake by promoting the secretion of saliva and gastric juice, resulting in an expansion of the stomach. In addition, hormone secretion is affected during fiber ingestion. Insulin response is reduced and cholecystokinin (CCK) in the small intestine is increased. Insulin regulates blood glucose levels while CCK adjusts gastric emptying, pancreatic secretion, and gall bladder contraction. There is a direct correlation between CCK and satiety after foods of different fiber contents are consumed.

In general, large intakes of dietary fiber at breakfast have been associated with less food intake at lunchtime. Fiber may have the added benefit of helping consumers reduce food intake throughout the day, but results of studies examining this possibility have been conflicting.

Increasing resistant starch intake

Resistant starch is a type of non-digestible, fermentable fiber resistant to amylase digestion in the small intestine. It is broken down to short-chain fatty acids by microflora in the large intestine. It is commonly found in cooked and cooled potatoes, green bananas, beans and legumes. The short chain fatty acids can lead to further oxidation of fat and a higher energy expenditure. Resistant starch dilutes energy density of food intake, maintains a bulking effect similar to non-fermentable fiber, and increases the expression of gut hormones PYY and GLP-1. The increase in gut hormone expression affects neuronal pathways in the brain that contribute to long-term energy balance and improved overall health of the intestines.

Increasing caffeine intake

Caffeine and black coffee have been associated with increased energy expenditure and subsequent weight loss. Caffeine belongs to a class of compounds called methylxanthines and is present in coffee, tea, cocoa, chocolate and some cola drinks. Caffeine induces a thermogenic effect in the body by increasing sympathetic nervous system activity, which is an important regulator of energy expenditure.

Increasing green tea intake

Green tea contains catechins that may aid weight loss.

Catechins are polyphenols that are a major component of green tea extract. Green tea has been associated with decreasing blood glucose, inhibiting hepatic and body fat accumulation, and stimulating thermogenesis due to the catechins present in formulations. Moreover, catechins in the brain play a major role in satiety. Independent of the caffeine content, green tea has also been shown to increase energy expenditure and fat oxidation in humans.

While green tea intake alone may not significantly reduce weight or BMI, combining intake with other strategies aimed at weight loss could be helpful for both loss and weight maintenance.

こちらも参照

• 抗肥満薬
• ダイエット
• Nutrigenomics/ja
• 栄養
• Weight loss/ja
• Weight gain/ja
• Orthorexia/ja

さらに読む

• Brownell KD (2004). The Learn Program for Weight Management: lifestyle, exercise, attitudes, relationships, nutrition (10th ed.). Dallas, Tex.: American Health Pub. Co. ISBN 978-1-878513-41-0.
• Dalton S (1997). Overweight and weight management: the health professional's guide to understanding and practice. Gaithersburg, Md.: Aspen Publishers. ISBN 978-0-8342-0636-6.
• Laliberte M, Taylor V, McCabe RE (2009). The cognitive behavioral workbook for weight management: a step-by-step program. Oakland, Calif.: New Harbinger Publications. ISBN 978-1-57224-625-6.
• Fulda J (2008). Half-Assed: A Weight-Loss Memoir. Berkeley, CA: Seal Press. ISBN 978-1-58005-278-8.
• Mann T (7 April 2015). Secrets From the Eating Lab: The Science of Weight Loss, the Myth of Willpower, and Why You Should Never Diet Again. HarperCollins. ISBN 978-0-06-232926-4.