Hooper Lee, Abdelhamid Asmaa S, Jimoh Oluseyi F, Bunn Diane, Skeaff C Murray
Norwich Medical School, University of East Anglia, Norwich, UK.
Human Nutrition, University of Otago, Dunedin, New Zealand.
Cochrane Database Syst Rev. 2020 Jun 1;6(6):CD013636. doi: 10.1002/14651858.CD013636.
The ideal proportion of energy from fat in our food and its relation to body weight is not clear. In order to prevent overweight and obesity in the general population, we need to understand the relationship between the proportion of energy from fat and resulting weight and body fatness in the general population.
To assess the effects of proportion of energy intake from fat on measures of body fatness (including body weight, waist circumference, percentage body fat and body mass index) in people not aiming to lose weight, using all appropriate randomised controlled trials (RCTs) of at least six months duration.
We searched CENTRAL, MEDLINE, Embase, Clinicaltrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) to October 2019. We did not limit the search by language.
Trials fulfilled the following criteria: 1) randomised intervention trial, 2) included adults aged at least 18 years, 3) randomised to a lower fat versus higher fat diet, without the intention to reduce weight in any participants, 4) not multifactorial and 5) assessed a measure of weight or body fatness after at least six months. We duplicated inclusion decisions and resolved disagreement by discussion or referral to a third party.
We extracted data on the population, intervention, control and outcome measures in duplicate. We extracted measures of body fatness (body weight, BMI, percentage body fat and waist circumference) independently in duplicate at all available time points. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity, funnel plot analyses and GRADE assessment.
We included 37 RCTs (57,079 participants). There is consistent high-quality evidence from RCTs that reducing total fat intake results in small reductions in body fatness; this was seen in almost all included studies and was highly resistant to sensitivity analyses (GRADE high-consistency evidence, not downgraded). The effect of eating less fat (compared with higher fat intake) is a mean body weight reduction of 1.4 kg (95% confidence interval (CI) -1.7 to -1.1 kg, in 53,875 participants from 26 RCTs, I = 75%). The heterogeneity was explained in subgrouping and meta-regression. These suggested that greater weight loss results from greater fat reductions in people with lower fat intake at baseline, and people with higher body mass index (BMI) at baseline. The size of the effect on weight does not alter over time and is mirrored by reductions in BMI (MD -0.5 kg/m, 95% CI -0.6 to -0.3, 46,539 participants in 14 trials, I = 21%), waist circumference (MD -0.5 cm, 95% CI -0.7 to -0.2, 16,620 participants in 3 trials; I = 21%), and percentage body fat (MD -0.3% body fat, 95% CI -0.6 to 0.00, P = 0.05, in 2350 participants in 2 trials; I = 0%). There was no suggestion of harms associated with low fat diets that might mitigate any benefits on body fatness. The reduction in body weight was reflected in small reductions in LDL (-0.13 mmol/L, 95% CI -0.21 to -0.05), and total cholesterol (-0.23 mmol/L, 95% CI -0.32 to -0.14), with little or no effect on HDL cholesterol (-0.02 mmol/L, 95% CI -0.03 to 0.00), triglycerides (0.01 mmol/L, 95% CI -0.05 to 0.07), systolic (-0.75 mmHg, 95% CI -1.42 to -0.07) or diastolic blood pressure(-0.52 mmHg, 95% CI -0.95 to -0.09), all GRADE high-consistency evidence or quality of life (0.04, 95% CI 0.01 to 0.07, on a scale of 0 to 10, GRADE low-consistency evidence).
AUTHORS' CONCLUSIONS: Trials where participants were randomised to a lower fat intake versus a higher fat intake, but with no intention to reduce weight, showed a consistent, stable but small effect of low fat intake on body fatness: slightly lower weight, BMI, waist circumference and percentage body fat compared with higher fat arms. Greater fat reduction, lower baseline fat intake and higher baseline BMI were all associated with greater reductions in weight. There was no evidence of harm to serum lipids, blood pressure or quality of life, but rather of small benefits or no effect.
食物中脂肪提供的能量的理想比例及其与体重的关系尚不清楚。为了预防普通人群超重和肥胖，我们需要了解普通人群中脂肪供能比例与体重及体脂之间的关系。
使用所有持续时间至少为六个月的适当随机对照试验（RCT），评估脂肪能量摄入量比例对非减重人群体脂测量指标（包括体重、腰围、体脂百分比和体重指数）的影响。
我们检索了截至2019年10月的Cochrane系统评价数据库、医学期刊数据库、Embase数据库、Clinicaltrials.gov和世界卫生组织国际临床试验注册平台（ICTRP）。我们没有对检索语言进行限制。
试验符合以下标准：1）随机干预试验；2）纳入年龄至少18岁的成年人；3）随机分配至低脂饮食组与高脂饮食组，且任何参与者均无减重意图；4）非多因素试验；5）至少六个月后评估体重或体脂测量指标。我们重复纳入决策，并通过讨论或咨询第三方解决分歧。
我们重复提取了关于人群、干预措施、对照措施和结局指标的数据。我们在所有可用时间点独立重复提取体脂测量指标（体重、体重指数、体脂百分比和腰围）。我们进行了随机效应荟萃分析、荟萃回归、亚组分析、敏感性分析、漏斗图分析和GRADE评估。
我们纳入了37项随机对照试验（57079名参与者）。随机对照试验提供了一致的高质量证据，表明减少总脂肪摄入量会导致体脂略有降低；几乎所有纳入研究均观察到这一点，且对敏感性分析具有高度抗性（GRADE高一致性证据，未降级）。与高脂饮食相比，低脂饮食的效果是平均体重减轻1.4千克（95%置信区间（CI）-1.7至-1.1千克，来自26项随机对照试验的53875名参与者，I² = 75%）。亚组分析和荟萃回归解释了异质性。这些分析表明，基线脂肪摄入量较低和基线体重指数（BMI）较高的人群，脂肪减少量越大，体重减轻越多。体重减轻的幅度不会随时间变化，体重指数（MD -0.5 kg/m²，95% CI -0.6至-0.3，14项试验中的46539名参与者，I² = 21%）、腰围（MD -0.5厘米，95% CI -0.7至-0.2，3项试验中的16620名参与者；I² = 21%）和体脂百分比（MD -0.3%体脂，95% CI -0.6至0.00，P = 0.05，2项试验中的2350名参与者；I² = 0%）的降低与之相符。没有迹象表明低脂饮食存在可能抵消其对体脂有益影响的危害。体重减轻反映在低密度脂蛋白（-0.13 mmol/L，95% CI -0.21至-0.05）和总胆固醇（-0.23 mmol/L，95% CI -0.32至-0.14）略有降低，而对高密度脂蛋白胆固醇（-0.02 mmol/L，95% CI -0.03至0.00）、甘油三酯（0.01 mmol/L，95% CI -0.05至0.07）、收缩压（-0.75 mmHg，95% CI -1.42至-0.07）或舒张压（-0.52 mmHg，95% CI -0.95至-0.09）几乎没有影响，所有这些均为GRADE高一致性证据，对生活质量也几乎没有影响（0.04，95% CI 0.01至0.07，评分范围为0至10，GRADE低一致性证据）。
将参与者随机分配至低脂摄入组与高脂摄入组但无减重意图的试验表明，低脂摄入对体脂有一致、稳定但较小的影响：与高脂组相比，体重、体重指数、腰围和体脂百分比略低。更大程度的脂肪减少、更低的基线脂肪摄入量和更高的基线BMI均与更大程度的体重减轻相关。没有证据表明低脂饮食对血脂、血压或生活质量有害，反而有一些小的益处或无影响。
