Background
Escalating rates of overweight and obesity are a threat to the health of billions of people across the globe. Obesity increases the risk of premature mortality and of many noncommunicable diseases (NCDs) including cardiovascular diseases (CVDs), type 2 diabetes and certain types of cancers; it also increases the risk of becoming severely ill from COVID-19.
Among other lifestyle and dietary factors, the macronutrient distribution of the diet (i.e. the percentage of carbohydrates, protein and fats) has been explored as a possible contributor to the development of overweight and obesity. Dietary fat and fatty acids are important in human physiology but are also the most energy dense of the macronutrients, and there has been extensive discussion of the potential impact of the percentage of calories consumed as fat on body weight. Because the role of dietary fat in the development of overweight and obesity continues to be debated, it was considered important to review the evidence in a systematic manner, and to update current WHO guidance on total fat through the WHO guideline development process.
Objective, scope and methods
The objective of this guideline is to provide updated guidance on the intake of total fat, to be used by policy-makers, programme managers, health professionals and other stakeholders in efforts to promote healthy diets. The guidance was formulated based on evidence for unhealthy weight gain1 only. The guideline was developed following the WHO guideline development process, as outlined in the WHO handbook for guideline development. This process includes a review of systematically gathered evidence by an international, multidisciplinary group of experts; assessment of the quality of that evidence via the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework; and consideration of additional, potentially mitigating factors2 when translating the evidence into recommendations. The guidance in this guideline replaces previous WHO guidance on total fat intake, including that from the 1989 WHO Study Group on Diet, Nutrition and the Prevention of Chronic Diseases and the 2002 Joint WHO/FAO Expert Consultation on Diet, Nutrition and the Prevention of Chronic Diseases.
The evidence
Evidence from a systematic review of randomized controlled trials (RCTs) conducted in non-dieting adults found that reducing intake of total fat led to lower body weight, body mass index (BMI), waist circumference and percentage of body fat (high certainty evidence overall). Results of subgroup analyses and meta-regression suggest that greater reductions in total fat intake were associated with greater differences in body weight, and that those consuming less than 30% of total energy intake as fat had less body fatness than those consuming 30% or more of total energy intake as fat. There was no suggestion of undesirable effects associated with reduced fat intake that might mitigate any benefits on body fatness, including undesirable changes in blood lipids or blood pressure or negative effects on quality of life. In fact, a small improvement in total cholesterol, low density lipoprotein (LDL) cholesterol and blood pressure was observed with reduced fat intake.
Because of differences in methodology and data reporting across the studies, meta-analyses of identified prospective cohort studies could not be reliably conducted. Of the 39 reported analyses in 14 cohort studies on the association between total fat intake and measures of body fatness in adults, 12 suggested a positive association, three suggested a negative association and one was unclear. The remaining 23 analyses did not show statistically significant associations.3
Three RCTs conducted in children were identified, but due to differential reporting of outcomes at different points of follow-up they were not considered suitable for meta-analysis. Results of RCTs on measures of body fatness were inconsistent but there was no suggestion of undesirable effects associated with reduced fat intake in terms of blood lipids or linear growth.
Recommendations and supporting information
These recommendations should be considered in the context of other WHO guidelines on healthy diets, including those on saturated fatty acids, trans-fatty acids, polyunsaturated fatty acids, sugars, carbohydrates, non-sugar sweeteners, sodium and potassium.
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| WHO recommendations |
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To reduce the risk of unhealthy weight gain, WHO suggests that adults limit total fat intake to 30% of total energy intake or less (conditional recommendation) Fat consumed should be primarily unsaturated fatty acids, with no more than 10% of total energy intake coming from saturated fatty acids and no more than 1% of total energy intake coming from trans-fatty acids (strong recommendation)
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Rationale for recommendation 1
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This recommendation is based on evidence of high certainty from a systematic review of RCTs of dietary fat reduction in adults in which weight loss was not an explicit goal. All measures of body fatness assessed in the review (i.e. body weight, BMI, waist circumference and percentage body fat) were lower in adult participants randomized to a lower fat intake versus usual or moderate intake, with the most commonly reported measure being body weight. The evidence further suggests that the greater the difference in fat intake between those reducing fat intake and those not doing so, the greater the difference in body weight (i.e. a dose–response relationship), regardless of the final level of total fat intake achieved. Overall, the evidence suggests that a lower fat intake has the potential to help reduce the risk of unhealthy weight gain.
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The threshold of 30% was selected because most of the trials included in the analyses reported total fat intakes of 30% or more at baseline (range: 29–43% of total energy intake) and most studies achieved intakes of 30% or less in the intervention arms (range: 14–35% of total energy intake). When compared directly via subgroup analysis, there was a greater difference in body weight in trials where total fat intake was reduced to a final level of less than 30% of total energy intake in the intervention arms than in trials where total fat intake was reduced to a final level that was 30% of total energy intake or more in the intervention arms. In addition, the observed dose–response relationship indicates a cumulative effect of lower fat intake across the range of baseline intakes, with a greater reduction in fat intake resulting in a greater difference in body weight. Therefore, although an effect on body weight is anticipated with reducing total fat intake regardless of the level of total fat intake achieved, the greatest effect may be achieved with a reduction to 30% of total energy intake or less.
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The recommendation was assessed as conditional because some individuals who reduce their fat intake might replace some of the energy from dietary fat with energy from foods that are undesirable from a dietary quality perspective (e.g. free sugars), reducing the net benefit. It is therefore important to consider this recommendation in the context of other WHO dietary recommendations, including those on free sugars and carbohydrates, which provide guidance on carbohydrate quality. The evidence did not suggest any undesirable effects with respect to serum lipids, blood pressure or quality of life from lower total fat intake, but rather of small benefits or no effect (all high certainty evidence, except for quality of life, which was assessed as low certainty evidence). No mitigating factors were identified that would argue against limiting total fat intake to 30% of total energy intake or less.
Remarks for recommendation 1
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This recommendation is relevant for individuals aged 20 years or older.
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The goal in developing this guideline was to provide recommendations for both adults and children. However, the evidence was considered insufficient to support the formulation of a recommendation for children owing to the limited number of studies and inconsistent results identified for children, and the conclusion that the adult data could not reasonably be extrapolated to children given the unique energy requirements for optimal growth and development throughout childhood and adolescence. Previous expert consultations on dietary fats have concluded that for children aged 6 months and above and adolescents, total fat intakes of up to 35% of total energy are appropriate to meet growth demands without leading to excess energy intake.4
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The threshold of 30% in this recommendation should not be interpreted as an upper value of intake to be achieved by increasing fat intake among those with nutritionally adequate total fat intakes that are already less than 30% of total energy intake.
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Evaluation of the evidence suggests that the observed effect of reducing total fat intake on measures of body fatness is mediated, at least in part, by dietary behaviours that affect energy balance. In most trials, those who reduced their total fat intake also decreased their total energy intake (even though that was not intended in the trial design), and this led to decreasing weight. This finding suggests that there may be a tendency for those habitually consuming greater amounts of total fat to also consume more energy than needed, resulting in excess energy intake and subsequent weight gain. However, individuals who can maintain energy balance (or otherwise prevent excess energy intake) at higher fat intakes may be able to consume total fat at levels greater than 30% of total energy intake without increasing their risk of unhealthy weight gain.
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The scope of this guideline was limited to developing recommendations for the prevention of unhealthy weight gain, not for the management of existing overweight or obesity. Therefore, studies conducted with overweight participants actively pursuing weight loss (i.e. “weight loss studies”) were not included in the systematic review used to inform the recommendation. The recommendation may therefore not apply to individuals actively pursuing weight loss through modification of the diet, although current evidence does suggest that lower fat, restricted-calorie diets may be one of several effective, short-term strategies for losing excess body weight.
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This recommendation should not be interpreted as implying that total fat is the only risk factor for unhealthy weight gain and that reducing total fat intake alone is sufficient to prevent unhealthy weight gain. The etiology of unhealthy weight gain is complex and can involve many different inputs. Therefore, this recommendation should be considered in the context of other relevant WHO guidance, including that on the intake of free sugars, carbohydrates, non-sugar sweeteners, energy requirements and physical activity.
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Dietary fat, including essential fatty acids (which cannot be synthesized by the human body), is necessary for proper physiological function. To ensure an adequate intake of energy and essential fatty acids, and to facilitate the absorption of lipid-soluble vitamins, total fat intake in most adults should be at least 15–20% of total energy intake.
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The decision to implement this recommendation must be made in the context of achieving or maintaining nutritional adequacy and avoiding excess energy intake. In populations where undernutrition is not prevalent, the recommendation can generally be safely implemented as needed, provided that individual energy requirements are met, and recognizing that energy requirements are increased in pregnant and lactating women. Consideration must be given to populations in which prevalence of undernutrition is a concern and where total fat intake may already be low. In such settings, maintaining or even increasing total fat intake of individuals (in line with guidance on fat quality in recommendation 2) may be important to achieve adequate energy intake, as well as maintain or improve the overall diet.
Rationale for recommendation 2
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This recommendation is taken from recommendations found in the WHO guideline, Saturated fatty acid and trans-fatty acid intake for adults and children which are based on effects of these nutrients on mortality and CVD outcomes.
Remarks for recommendation 2
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This recommendation is relevant for all individuals aged 2 years and older.
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This recommendation, taken together with recommendation 1, acknowledges that both quantity and quality of fat consumed are important for health and nutritional well-being.
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Further remarks may be found in the WHO guideline, Saturated fatty acid and trans-fatty acid intake for adults and children.
- 1
In this context, unhealthy weight gain refers to unintentional weight gain (i.e. increase in body fatness) that contributes to the progression towards overweight and obesity, but excludes appropriate weight gain during pregnancy and as part of normal growth and development in childhood. Other exceptions would include weight gain resulting from activities that increase muscle mass without increasing fat mass, such as weight-lifting and other strength-building exercise. For the development of this guideline, unhealthy weight gain was assessed as an increase in, or greater measures of, body fatness as reported in the systematic reviews underpinning the recommendations.
- 2
These include desirable and undesirable effects of the intervention, priority of the problem that the recommendations address, values and preferences related to the recommendations in different settings, the cost of the options available to public health officials and programme managers in different settings, feasibility and acceptability of implementing the recommendations in different settings, and the potential impact on equity and human rights.
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The evidence from cohort studies was reviewed but was not formally assessed for quality using GRADE methodology, given the inability to pool the effects of the identified cohort studies via meta-analysis, that the qualitative results from the cohort studies were consistent with those from the RCTs and that the data from the RCTs were robust and of higher certainty.
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Infants should be exclusively breastfed for the first 6 months of life to achieve optimal growth, development and health. Thereafter, to meet their evolving nutritional requirements, infants should receive nutritionally adequate and safe complementary foods, while continuing to breastfeed for up to 2 years or beyond.
