ダイエット

ダイエットとは、体重の減少、維持、増加、あるいは糖尿病や肥満などの病気の予防や治療のために、食事を規則正しく行うことである。減量はカロリー摂取量に依存するため、特定の大栄養素を強調したもの（低脂肪、低炭水化物など）などのカロリー低減ダイエットのさまざまな種類は、互いにそれ以上の効果がないことが示されている。

最初に流行したダイエット法は「バンティング」で、ウィリアム・バンティングにちなんで名付けられた。1863年の小冊子『大衆に宛てた肥満に関する手紙』の中で、彼は特定の低炭水化物、低カロリー食の詳細を概説し、彼自身の劇的な体重減少につながった。

いくつかのガイドラインでは、体重に関連した健康問題を抱える人には減量のためのダイエットを勧めているが、そうでない健康な人には勧めていない。 ある調査によると、アメリカの成人のほぼ半数がダイエットによる減量を試みており、その中には肥満の成人の66.7％、標準体重または低体重の成人の26.5％が含まれている。肥満でない）過体重、標準体重、または低体重のダイエッターは、ダイエットの結果として死亡率が増加する可能性がある。

歴史

ウィリアム・バンティングは、19世紀に最初の減量ダイエットのひとつを普及させた。

ダイエットという言葉はギリシャ語の「δίαιτα (diaita)」に由来しており、狭い意味での減量法ではなく、精神的・肉体的な健康も含めた全体的な健康的なライフスタイルという概念を表している。

最初の栄養学者の一人は、イギリスの医師ジョージ・チェインだった。彼自身はとてつもなく太りすぎで、常に大量の豊かな食べ物や飲み物を口にしていた。彼は肉を食べない食事療法を始め、牛乳と野菜だけを摂取し、すぐに健康を取り戻した。彼は、肥満のすべての人に自分の食事法を公に勧め始めた。1724年、彼はAn Essay of Health and Long Lifeを書き、その中で運動と新鮮な空気、贅沢な食べ物を避けることを勧めている。

スコットランドの軍医John Rolloは1797年にNotes of a Diabetic Caseを出版した。このノートでは糖尿病の患者に対する肉食の利点が述べられており、この推奨はマシュー・ドブソンによる糖尿病における糖尿の発見に基づくものであった。ドブソンの検査方法（尿中のグルコースの検査）によって、Rolloは現在2型糖尿病と呼ばれているものに成功する食事療法を考案した。

最初に流行したダイエット法は「バンティング」で、イギリスの葬儀屋ウィリアム・バンティングにちなんで名付けられた。1863年、彼はLetter on Corpulence, Addressed to the Publicという小冊子を書いた。彼自身の食事は1日4食で、肉、青菜、果物、辛口のワインから成っていた。砂糖、甘いもの、でんぷん、ビール、牛乳、バターを避けることに重点を置いていた。バンティングのパンフレットはその後何年も人気を博し、現代の食生活のモデルとして使われることになる。このパンフレットの人気は、"Do you bant?"という質問が彼の方法を指すようになり、やがてダイエット全般を指すようになった。彼の小冊子は2007年現在も印刷されている。

カロリー計算を推進した最初の減量本であり、ベストセラーになった最初の減量本は、アメリカの医師でコラムニストのルル・ハント・ピーターズによる1918年のダイエットと健康：カロリーの鍵であった。

2014年までに1000以上のダイエット法が開発されたと推定されている。

種類

食事制限ダイエットは、減量したい人が最もよく行う。体重を増やすために食事療法を行う人もいる（体重が少ない人や、筋肉を増やそうとしている人など）。ダイエットはまた、安定した体重を維持するためや、健康を改善するために行われることもある。

低脂肪

詳細は「Low-fat diet/ja」を参照

低脂肪ダイエットでは、食事に含まれる脂肪の割合を減らす。脂肪の摂取量が減るため、カロリー消費量が減る。このタイプの食事療法にはNCEPステップIとIIがある。2～12ヵ月間の16の臨床試験のメタアナリシスによると、低脂肪食（意図的なカロリー摂取制限なし）は習慣的な食事よりも平均3.2 kg (7.1 lb)の体重減少をもたらした。

低脂肪で植物ベースの食事は、体重、血糖値、心臓血管の健康のコントロールを改善することが判明している。

低炭水化物

This section is an excerpt from 低炭水化物ダイエット.[編集]

低炭水化物料理の一例、調理したケールとポーチドエッグ

低炭水化物ダイエットでは、平均的なダイエットと比較して炭水化物の消費を制限する。炭水化物を多く含む食品（例えば、砂糖、パン、パスタ）を制限し、脂肪とタンパク質の割合が高い食品（例えば、 肉、鶏肉、魚、貝類、卵、チーズ、ナッツ、種子）や低炭水化物食品（例． 例えばほうれん草、ケール、チャード、コラード、その他の繊維質の野菜）。

低炭水化物食の炭水化物摂取量については標準化がなされていないため、研究が複雑になっている。アメリカ家庭医学会の定義のひとつでは、低炭水化物食とは、炭水化物からのカロリーが20％未満であることとしている。

低炭水化物ダイエットが体重減少を除けば、特定の健康上の利益をもたらすという良い証拠はない。体重減少は主にカロリー制限とその遵守によって決まるため、低炭水化物ダイエットは他のダイエットと同様の結果をもたらす。

低炭水化物食の1つであるケトジェニックダイエットは、てんかんを治療するための医薬品として最初に確立された。それは有名人の推薦によって減量のための人気のある食事療法となったが、この目的のための際立った利点の証拠はなく、この食事療法は副作用のリスクを伴い、英国栄養士会は2018年に「避けるべき最悪のセレブダイエットトップ5」の1つに挙げた。

低カロリー

詳細は「Calorie restriction/ja」を参照

低カロリーダイエットは通常、1日あたり500～1,000キロカロリーのエネルギー不足を生じさせ、1週間あたり0.5 to 1 kilogram (1.1 to 2.2 pounds)の体重減少をもたらす。米国国立衛生研究所は、低カロリー食の有効性を判断するために34のランダム化比較試験を検討した。その結果、これらのダイエットは3～12ヵ月の短期間で総体量を8％低下させることがわかった。低カロリー食を行う女性は1日あたり少なくとも1,000キロカロリー、男性は1日あたり約1,200キロカロリー摂取する必要がある。これらの摂取カロリーの値は、年齢や体重などの追加要因によって異なる。

超低カロリー

詳細は「Very low calorie diet/ja」を参照

超低カロリー食は1日200～800キロカロリーで、タンパク質の摂取は維持するが、脂肪と炭水化物の両方のカロリーを制限する。これらは身体を飢餓状態にさらし、1週間に平均1.5–2.5 kg (3.3–5.5 lb)の損失をもたらす。"2-4-6-8 "は、この種のダイエットとして人気があり、初日は200キロカロリー、2日目は400キロカロリー、3日目は600キロカロリー、4日目は800キロカロリーしか摂取せず、その後完全に絶食する、というサイクルを4日間繰り返す。これらのダイエットでかなりの減量につながるという証拠もある。これらの食事療法は、除脂肪体重の減少、痛風のリスク増加、電解質不均衡などの副作用を伴うため、一般的な使用には推奨されず、肥満の管理にとどめるべきである。これらのダイエットを試みる人は、合併症を防ぐために医師によって注意深く監視されなければならない。

クラッシュダイエットのコンセプトは、超低カロリー食でカロリーを大幅に減らすことだ。クラッシュダイエットは、人体にさまざまな問題を引き起こす可能性があるため、非常に危険である。クラッシュダイエットは体重を減少させることができるが、専門家の監視がなければ、カロリーの極端な減少や食事構成のバランスが崩れる可能性があり、突然死を含む有害な影響を引き起こす可能性がある。

Fasting

Main articles: Fasting and Intermittent fasting

Fasting is the act of intentional taking a long time interval between meals. Lengthy fasting (multiple days in a week) might be dangerous due to the risk of malnutrition. During prolonged fasting or very low calorie diets the reduction of blood glucose, the preferred energy source of the brain, causes the body to deplete its glycogen stores. Once glycogen is depleted the body begins to fuel the brain using ketones, while also metabolizing body protein (including but not limited to skeletal muscle) to be used to synthesize sugars for use as energy by the rest of the body. Most experts believe that a prolonged fast can lead to muscle wasting, although some dispute this. The use of short-term fasting, or various forms of intermittent fasting, have been used as a form of dieting to circumvent the issues of long fasting.

Intermittent fasting commonly takes the form of periodic fasting, alternate-day fasting, time-restricted feeding, and/or religious fasting. It can be a form of reduced-calorie dieting but pertains entirely to when the metabolism is activated during the day for digestion. The changes to eating habits on a regular basis do not have to be severe or absolutely restrictive to see benefits to cardiovascular health, such as improved glucose metabolism, reduced inflammation, and reduced blood pressure. Studies have suggested that for people in intensive care, an intermittent fasting regimen might "[preserve] energy supply to vital organs and tissues... [and] powerfully activates cell-protective and cellular repair pathways, including autophagy, mitochondrial biogenesis and antioxidant defenses, which may promote resilience to cellular stress." The effects of decreased serum glucose and depleted hepatic glycogen causing the body to switch to ketogenic metabolism are similar to the effects of reduced carbohydrate-based diets. There is evidence demonstrating profound metabolic benefits of intermittent fasting in rodents. However, evidence is lacking or contradictory in humans and requires further investigation, especially over the long-term. Some evidence suggests that intermittent restriction of caloric intake has no weight-loss advantages over continuous calorie restriction plans. For adults, fasting diets appear to be safe and tolerable, however there is a possibility that periods of fasting and hunger could lead to overeating and to weight regain after the fasting period. Adverse effects of fasting are often moderate and include halitosis, fatigue, weakness, and headaches. Fasting diets may be harmful to children and the elderly.

Exclusion Diet

This type of diet is based on the restriction of specific foods or food groups. Examples include gluten-free, Paleo, plant-based, and Mediterranean diets.

Plant-based diets include vegetarian and vegan diets, and can range from the simple exclusion of meat products to diets that only include raw vegetables, fruits, nuts, seeds, legumes, and sprouted grains. Exclusion of animal products can reduce the intake of certain nutrients, which might lead to nutritional deficiencies of protein, iron, zinc, calcium, and vitamins D and B₁₂. Therefore, long term implementation of a plant-based diet requires effective counseling and nutritional supplementation as necessary. Plant-based diets are effective for short-term treatment of overweight and obesity, likely due to the high consumption of low energy density foods. However, evidence for long-term efficacy is limited.

The Paleo diet includes foods that were available to our hunter-gatherer ancestors including meat, nuts, eggs, some oils, fresh fruits, and vegetables. Overall, it is high in protein and moderate in fats and carbohydrates. Some limited evidence suggests various health benefits and effective weight loss with this diet. However, similar to the plant-based diet, the Paleo diet has potential nutritional deficiency risks, specifically with vitamin D, calcium, and iodine.

Gluten-free diets are often used for weight loss but little has been studied about the efficacy of this diet and metabolic mechanism for its effectiveness is unclear.

The Mediterranean diet is characterized by high consumption of vegetables, fruits, legumes, whole-grain cereals, seafood, olive oil, and nuts. Red meat, dairy and alcohol are only recommended in moderation. Studies show that the Mediterranean diet is associated with short term as well as long term weight loss in addition to health and metabolic benefits.

Detox

Main article: Detox diet

Detox diets are promoted with unsubstantiated claims that they can eliminate "toxins" from the human body. Many of these diets use herbs or celery and other juicy low-calorie vegetables. Detox diets can include fasting or exclusion (as in juice fasting). Detox diets tend to result in short-term weight loss (because of calorie restriction), followed by weight gain.

Environmentally sustainable

See also: Environmental vegetarianism

Another kind of diet focuses not on the dieter's health effects, but on its environment. The One Blue Dot plan of the BDA offers recommendations towards reducing diets' environmental impacts, by:

1. Reducing meat to 70g per person per day.
2. Prioritising plant proteins.
3. Promoting fish from sustainable sources.
4. Moderate dairy consumption.
5. Focusing on wholegrain starchy foods.
6. Promoting seasonal locally sourced fruits and vegetables.
7. Reducing high fat, sugar and salty foods overconsumption.
8. Promoting tap water and unsweetened tea/coffee as the de facto choice for healthy hydration.
9. Reducing food waste.

Effectiveness

Several diets are effective for short-term weight loss for obese individuals, with diet success most predicted by adherence and little effect resulting from the type or brand of diet. As weight maintenance depends on calorie intake, diets emphasising certain macronutrients (low-fat, low-carbohydrate, etc.) have been shown to be no more effective than one another and no more effective than diets that maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). A meta-analysis of six randomized controlled trials found no difference between low-calorie, low-carbohydrate, and low-fat diets in terms of short-term weight loss, with a 2–4 kilogram weight loss over 12–18 months in all studies. Diets that severely restrict calorie intake do not lead to long term weight loss. Extreme diets may, in some cases, lead to malnutrition.

A major challenge regarding weight loss and dieting relates to compliance. While dieting can effectively promote weight loss in the short term, the intervention is hard to maintain over time and suppresses skeletal muscle thermogenesis. Suppressed thermogenesis accelerates weight regain once the diet stops, unless that phase is accompanied by a well-timed exercise intervention, as described by the Summermatter cycle. Most diet studies do not assess long-term weight loss.

Some studies have found that, on average, short-term dieting results in a "meaningful" long-term weight-loss, although limited because of gradual 1 to 2 kg/year weight regain. Because people who do not participate in weight-loss programs also tend to gain weight over time, and baseline data from such "untreated" participants are typically not included in diet studies, it is possible that diets do result in lower weights in the long-term relative to people who do not diet. Others have suggested that dieting is ineffective as a long-term intervention. For each individual, the results will be different, with some even regaining more weight than they lost, while a few others achieve a tremendous loss, so that the "average weight loss" of a diet is not indicative of the results other dieters may achieve. A 2001 meta-analysis of 29 American studies found that participants of structured weight-loss programs maintained an average of 23% (3 kg) of their initial weight loss after five years, representing a sustained 3.2% reduction in body mass. Unfortunately, patients are generally unhappy with weight loss of <10%, and reductions even as high as 10% are insufficient for changing someone with an "obese" BMI to a "normal weight" BMI.

Partly because diets do not reliably produce long-term positive health outcomes, some argue against using weight loss as a goal, preferring other measures of health such as improvements in cardiovascular biomarkers, sometimes called a Health at Every Size (HAES) approach or a "weight neutral" approach.

Long term losses from dieting are best maintained with continuing professional support, long term increases in physical activity, the use of anti-obesity medications, continued use of meal replacements, and additional periods of dieting to undo weight regain. The most effective approach to weight loss is an in-person, high-intensity, comprehensive lifestyle intervention: overweight or obese adults should maintain regular (at least monthly) contact with a trained interventionalist who can help them engage in exercise, monitor their body weight, and reduce their calorie consumption. Even with high-intensity, comprehensive lifestyle interventions (consisting of diet, physical exercise, and bimonthly or even more frequent contact with trained interventionists), gradual weight regain of 1–2 kg/year still occurs. For patients at high medical risk, bariatric surgery or medications may be warranted in addition to the lifestyle intervention, as dieting by itself may not lead to sustained weight loss.

Many studies overestimate the benefits of calorie restriction because the studies confound exercise and diet (testing the effects of diet and exercise as a combined intervention, rather than the effects of diet alone).

Adverse effects

Increased mortality rate

A number of studies have found that intentional weight loss is associated with an increase in mortality in people without weight-related health problems. A 2009 meta-analysis of 26 studies found that "intentional weight loss had a small benefit for individuals classified as unhealthy (with obesity-related risk factors), especially unhealthy obese, but appeared to be associated with slightly increased mortality for healthy individuals, and for those who were overweight but not obese."

Dietary supplements

Due to extreme or unbalanced diets, dietary supplements are sometimes taken in an attempt to replace missing vitamins or minerals. While some supplements could be helpful for people eating an unbalanced diet (if replacing essential nutrients, for example), overdosing on any dietary supplement can cause a range of side effects depending on the supplement and dose that is taken. Supplements should not replace foods that are important to a healthy diet.

Eating disorders

In an editorial for Psychological Medicine, George Hsu concludes that dieting is likely to lead to the development of an eating disorder in the presence of certain risk factors. A 2006 study found that dieting and unhealthy weight-control behaviors were predictive of obesity and eating disorders five years later, with the authors recommending a "shift away from dieting and drastic weight-control measures toward the long-term implementation of healthful eating and physical activity".

Mechanism

When the body is expending more energy than it is consuming (e.g. when exercising), the body's cells rely on internally stored energy sources, such as complex carbohydrates and fats, for energy. The first source to which the body turns is glycogen (by glycogenolysis). Glycogen is a complex carbohydrate, 65% of which is stored in skeletal muscles and the remainder in the liver (totaling about 2,000 kcal in the whole body). It is created from the excess of ingested macronutrients, mainly carbohydrates. When glycogen is nearly depleted, the body begins lipolysis, the mobilization and catabolism of fat stores for energy. In this process fats, obtained from adipose tissue, or fat cells, are broken down into glycerol and fatty acids, which can be used to generate energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.

Set-Point Theory

See also: Energy homeostasis § Imbalance

The Set-Point Theory, first introduced in 1953, postulated that each body has a preprogrammed fixed weight, with regulatory mechanisms to compensate. This theory was quickly adopted and used to explain failures in developing effective and sustained weight loss procedures. A 2019 systematic review of multiple weight change procedures, including alternate day fasting and time-restricted feeding but also exercise and overeating, found systematic "energetic errors" for all these procedures. This shows that the body cannot precisely compensate for errors in energy/calorie intake, countering the Set-Point Theory and potentially explaining both weight loss and weight gain such as obesity. This review was conducted on short-term studies, therefore such a mechanism cannot be excluded in the long term, as evidence is currently lacking on this timeframe.

Methods

Meals timing

Meals timing schedule is known to be an important factor of any diet. Recent evidence suggest that new scheduling strategies, such as intermittent fasting or skipping meals, and strategically placed snacks before meals, may be recommendable to reduce cardiovascular risks as part of a broader lifestyle and dietary change.

Food diary

A 2008 study published in the American Journal of Preventive Medicine showed that dieters who kept a daily food diary (or diet journal), lost twice as much weight as those who did not keep a food log, suggesting that if a person records their eating, they are more aware of what they consume and therefore eat fewer calories.

Water

Main article: Weight loss effects of water

A 2009 review found limited evidence suggesting that encouraging water consumption and substituting energy-free beverages for energy-containing beverages (i.e., reducing caloric intake) may facilitate weight management. A 2009 article found that drinking 500 ml of water prior to meals for a 12-week period resulted in increased long-term weight reduction. (References given in main article.)

Society

It is estimated that about 1 out of 3 Americans is dieting at any given time. 85% of dieters are women. Approximately sixty billion dollars are spent every year in the USA on diet products, including "diet foods," such as light sodas, gym memberships or specific regimes. 80% of dieters start by themselves, whereas 20% see a professional or join a paid program. The typical dieter attempts 4 tries per year.

減量グループ

減量グループには金儲けを目的とするものもあれば、慈善事業として活動するものもある。前者にはWeight WatchersやPeertrainerがある。後者にはOvereaters Anonymousやen:TOPS ClubTOPS Club、地域の団体が運営するグループなどがある。

これらの組織の習慣や実践は大きく異なる。十二段階プログラムをモデルにしているグループもあれば、きわめて非公式なグループもある。特定の惣菜や特別メニューを提唱するグループもあれば、レストランのメニューから健康的な選択をしたり、食料品店での買い物や調理中にダイエッターを訓練するグループもある。

1対1のサポートを受けるよりも、体重減少プログラムのグループミーティングに参加した方が、肥満の人が体重を減らす可能性が高まるかもしれない。グループに参加した人は、治療時間が長く、健康状態を改善するのに十分な体重を減らす可能性が高かった。研究著者らは、この違いの説明の一つとして、グループ参加者は1対1のサポートを受けた人よりも、臨床医（またはプログラムを提供した人）と過ごす時間が長いことを示唆している。

こちらも参照

• Body image/ja
• Carbon footprint/ja
• Dietary Guidelines for Americans/ja
• Food faddism/ja
• High residue diet/ja
• Intuitive eating/ja
• List of diets/ja
• National Weight Control Registry/ja
• Nutrigenomics/ja
• Nutrition psychology/ja
• Nutrition scale/ja
• Nutritional rating systems/ja
• Online weight loss plans/ja
• Superfood/ja
• Table of food nutrients/ja
• Underweight/ja

さらに読む

• American Dietetic Association (June 2003). "Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets". Journal of the American Dietetic Association. 103 (6): 748–765. doi:10.1053/jada.2003.50142. PMID 12778049.
• Cheraskin E (1993). "The Breakfast/Lunch/Dinner Ritual". Journal of Orthomolecular Medicine. 8 (1).
• Dansinger ML, Gleason JL, Griffith JL, Li WJ, Selker HP, Schaefer EJ (12 November 2003). One Year Effectiveness of the Atkins, Ornish, Weight Watchers, and Zone Diets in Decreasing Body Weight and Heart Disease Risk. American Heart Association Scientific Sessions. Orlando, Florida.
• Schwartz, Hillel. Never Satisfied: A Cultural History of Diets, Fantasies, and Fat. New York: Free Press/Macmillan, 1986.

外部リンク

• Diet reviews by the Harvard School of Public Health