Att äta för lite kolhydrater kan förkorta livet med upp till fyra år. Måttliga mängder tycks vara det mest optimala. Då lever du längst, visar ny forskning.
I flera av de dieter som florerar just nu är kolhydraterna – som det finns mycket av i livsmedel såsom ris, pasta och potatis – i skottlinjen. I den så kallade LCHF-dieten, efter engelskans low carb, high fat, är tanken är hålla nere antalet kolhydrater på ett minimum och i stället äta mer animaliskt eller mättat fett, som smör, ost och grädde. Animaliska proteiner, som det finns gott om i kött, går också bra.
Tidigare randomiserade studier, där deltagarna lottats till olika grupper, har visat att metoden – i ett kortare tidsperspektiv – är hyfsat effektiv för att få till en viktminskning och att den metaboliska riskprofilen för hjärtsjukdom förbättras.
Den långsiktiga effekten av denna diet är däremot mer kontroversiell så tillvida att olika studier visar motstridiga resultat.
I ett försök att få veta mer har forskare i USA analyserat utfallet för de 15 428 personer som inkluderades i en hälsostudie mellan åren 1987 och 1989. Deltagarna var då mellan 45 och 64 år gamla och vid starten och sex år senare fick de fylla i ett frågeformulär om vad de åt och drack samt hur stora deras portioner var. Den genomsnittliga uppföljningsperioden var 25 år, under vilken 6 283 personer dog.
Efter att ha tagit hänsyn till en rad olika faktorer – som motion, ålder, rökning samt utbildning – analyserade forskarna om risken att dö påverkades av deras intag av kolhydrater.
Resultatet blev en U-formad kurva där personer vars kaloriintag till mindre andel (mindre än 40 procent) eller till större andel (mer än 70 procent) bestod av kolhydrater hade en högre risk att dö, jämfört med personer som åt mer måttliga mängder kolhydrater (50–55 procent av det totala kaloriintaget).
Enligt forskarna går resultaten, som presenteras i tidskriften The Lancet, att översätta med att från 50 års ålder så har en person med ett måttligt kolhydratintag i genomsnitt 33 år kvar att leva. En lika gammal person, fast med ett mycket lågt intag, kan förväntas leva 29 år till, medan en person som har ett högt intag i snitt får ytterligare 32 år.
– Låg-kolhydrat-dieter där kolhydraterna ersätts med protein eller fett blir allt populärare. Men våra data tyder på att dessa dieter kan förkorta livslängden och bör därför inte uppmuntras, säger en av artikelförfattarna, Sara Seidelman vid Briham and Women’s Hospital i Boston, till tidskriften.
Från TT 180818
Too much carbohydrate in the diet is bad, but too little may be unhealthy as well, researchers reported.
In a pooled meta-analysis of eight cohort studies that included more than 400,000 participants, a high-carb diet (more than 70% of energy from carbs) was associated with increased mortality risk (hazard ratio 1.23; 95% CI 1.11-1.36). But a low-carb diet (less than 40% carbs) was associated with nearly the same mortality risk increase (HR 1.20; 95% CI 1.09-1.32), according to a research team led by Sara Siedelmann, MD, of Brigham and Women's Hospital in Boston.
A diet in which 50%-55% of total energy came from carbohydrates was associated with minimal mortality risk, Siedelmann's group reported online in The Lancet Public Health.
"Our findings suggest a U-shaped relationship between life expectancy and overall carbohydrate intake, in which lifespan is greatest among people with 50%-55% carbohydrate intake, a level that might be considered moderate in North America and Europe but low in other regions, such as Asia," the study authors wrote.
In a smaller pooled analysis of three cohort studies that included more than 150,000 participants, the researchers found that when individuals exchanged carbohydrates for animal-derived sources of protein, such as beef, pork, or chicken, their mortality risk increased (HR 1.18; 95% CI 1.08-1.29). However, when carbs were exchanged for plant-based proteins, from sources including vegetables, nuts, and whole-grain breads, mortality risk decreased (HR 0.82; 95% 0.78-0.87).
"Low carbohydrate diets that exchange carbohydrates for a greater intake of protein or fat have gained substantial popularity because of their ability to induce short-term weight loss, despite incomplete and conflicting data regarding their long-term effects on health outcomes," the study authors wrote.
"These data provide further evidence that animal-based low carbohydrate diets, which are more prevalent in North American and European populations, should be discouraged," they said. "Alternatively, if restricting carbohydrate intake is a chosen approach for weight loss or cardiometabolic risk reduction, replacement of carbohydrates with predominantly plant-based fats and proteins could be considered as a long-term approach to promote healthy aging."
The investigators initially analyzed data from 15,428 U.S. adults age 45-64 who were part of the Atherosclerosis Risk in Communities (ARIC) study. The study is an ongoing prospective analysis of cardiovascular risk factors in four U.S. communities: Forsyth County North Carolina; Jackson Mississippi; suburbs of Minneapolis, Minnesota; and Washington County, Maryland. Participants completed an interview that included a 66-item food frequency questionnaire at enrollment in 1987-89 and again in 1993-95. The main outcome was all-cause mortality over 25 years of follow-up, and it was here that the investigators first noticed the U-shaped relationship between carbohydrate intake and life expectancy.
To confirm and extend these initial findings, the investigators pooled data from the ARIC study with data from seven other prospective cohort studies. These studies included the European Investigation into Cancer and Nutrition (ERIC) study, the Nurses' Health Study (NHS), and the Health Professionals Follow-up Study (HPFS). The pooled analysis included 432,179 participants. In all analyses, the investigators adjusted for factors including age, gender, race, education, smoking status, and physical activity.
One explanation for the link between low carbs and higher mortality, the study authors said, is that low-carbohydrate diets tend to result in reduced intakes of vegetables, fruits, and grains and increased intake of animal-based proteins. "Long-term effects of a low carbohydrate diet with typically low plant and increased animal protein and fat consumption have been hypothesized to stimulate inflammatory pathways, biological aging, and oxidative stress," they said.
"On the other end of the spectrum, high carbohydrate diets, which are common in Asian and less economically advantaged nations, tend to be high in refined carbohydrates, such as white rice; these types of diets might reflect poor food quality and confer a chronically high glycemic load that can lead to negative metabolic consequences," they said.
In an accompanying editorial, Andrew Mente, PhD, and Salim Yusuf, MD, both of McMaster University in London, Ontario, said the findings made a priori sense.
"Based on first principles, a U-shaped association is logical between most essential nutrients versus health outcomes. Essential nutrients should be consumed above a minimal level to avoid deficiency and below a maximal level to avoid toxicity. This approach maintains physiological processes and health (i.e., a so-called sweet spot)," they wrote.
"Although carbohydrates are technically not an essential nutrient (unlike protein and fats), a certain amount is probably required to meet short-term energy demands during physical activity and to maintain fat and protein intakes within their respective sweet spots," the editorial said. "On the basis of these principles, moderate intake of carbohydrate (eg, roughly 50% of energy) is likely to be more appropriate for the general population than are very low or very high intakes."
A limitation of the study, the authors said, was that it focused only on general carbohydrate intake and not the specific components of participants' diets. "Any number and combination of dietary components could have been considered and adjusted for in this analysis; therefore, some confounders might have been unadjusted for," they said.
The study was supported by the National Institutes of Health.
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The Lancet Public Health
Source Reference: Siedelmann SB, et al "Dietary carbohydrate intake and mortality: A prospective cohort study and meta-analysis" The Lancet Public Health 2018; DOI: 10.1016/S2468-2667(18)30135-X.Secondary Source
Low carbohydrate diets, which restrict carbohydrate in favour of increased protein or fat intake, or both, are a popular weight-loss strategy. However, the long-term effect of carbohydrate restriction on mortality is controversial and could depend on whether dietary carbohydrate is replaced by plant-based or animal-based fat and protein. We aimed to investigate the association between carbohydrate intake and mortality.
We studied 15 428 adults aged 45–64 years, in four US communities, who completed a dietary questionnaire at enrolment in the Atherosclerosis Risk in Communities (ARIC) study (between 1987 and 1989), and who did not report extreme caloric intake (<600 kcal or >4200 kcal per day for men and <500 kcal or >3600 kcal per day for women). The primary outcome was all-cause mortality. We investigated the association between the percentage of energy from carbohydrate intake and all-cause mortality, accounting for possible non-linear relationships in this cohort. We further examined this association, combining ARIC data with data for carbohydrate intake reported from seven multinational prospective studies in a meta-analysis. Finally, we assessed whether the substitution of animal or plant sources of fat and protein for carbohydrate affected mortality.
During a median follow-up of 25 years there were 6283 deaths in the ARIC cohort, and there were 40 181 deaths across all cohort studies. In the ARIC cohort, after multivariable adjustment, there was a U-shaped association between the percentage of energy consumed from carbohydrate (mean 48·9%, SD 9·4) and mortality: a percentage of 50–55% energy from carbohydrate was associated with the lowest risk of mortality. In the meta-analysis of all cohorts (432 179 participants), both low carbohydrate consumption (<40%) and high carbohydrate consumption (>70%) conferred greater mortality risk than did moderate intake, which was consistent with a U-shaped association (pooled hazard ratio 1·20, 95% CI 1·09–1·32 for low carbohydrate consumption; 1·23, 1·11–1·36 for high carbohydrate consumption). However, results varied by the source of macronutrients: mortality increased when carbohydrates were exchanged for animal-derived fat or protein (1·18, 1·08–1·29) and mortality decreased when the substitutions were plant-based (0·82, 0·78–0·87).
Both high and low percentages of carbohydrate diets were associated with increased mortality, with minimal risk observed at 50–55% carbohydrate intake. Low carbohydrate dietary patterns favouring animal-derived protein and fat sources, from sources such as lamb, beef, pork, and chicken, were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality, suggesting that the source of food notably modifies the association between carbohydrate intake and mortality.
National Institutes of Health.
The Lancet Public Health
Source Reference: Mente A, Yusuf S "Evolving evidence about diet and health" The Lancet Public Health 2018; DOI: 10.1016/S2468-2667(18)30160-9.