Low-fat diet
Eating less fat lowered weight about 1.4 kg and LDL slightly in people not trying to lose weight. In weight-loss trials, low-carbohydrate diets lost about 1 to 2 kg more. In a trial of 48,835 older women, heart disease, stroke, breast cancer and diabetes did not differ from usual diet. Triglycerides and HDL changed less than on low-carbohydrate diets.
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- Status
- A dietary pattern, not a regulated product.
- Also called
- low fat diet, low-fat eating, reduced-fat diet, fat-restricted diet, very low-fat diet, low-fat high-carbohydrate diet, Women's Health Initiative diet
- Followed for
- weight loss, heart health, cholesterol, breast cancer prevention, diabetes prevention
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help2
Reported risks2
- StrongShown to lower triglycerides less and raise HDL less than low-carbohydrate diets, in three meta-analyses of adults.How often is not known
- LimitedOne large trial found more ischemic stroke in healthy women with normal blood pressure, and more coronary heart disease in women who had heart disease at entry.How often is not known
What people follow it for, and what was found
Shown to help2
Body weight without trying to lose weight
Shown to lower body weight about 1.4 kg against higher-fat diets in adults not trying to lose weight, with larger drops at higher starting BMI.
Compared with diets with more fat
The numbers and sources
- Effect
- Across 37 RCTs (57,079 participants) lasting at least 6 months, eating less fat lowered body weight 1.4 kg against higher fat intake (95% CI 1.1 to 1.7, 26 RCTs, 53,875 participants, I² 75%), BMI 0.5 kg/m² and waist 0.5 cm. Greater fat reduction, lower baseline fat intake and higher baseline BMI went with larger losses [1]. In postmenopausal women given no weight or calorie goals, the low-fat group lost 2.2 kg in the first year and stayed lighter than controls, by 1.9 kg at 1 year and 0.4 kg at 7.5 years [2].
- Population
- Adults randomized to lower or higher fat intake with no weight-loss aim [1]; 48,835 postmenopausal women aged 50 to 79 in the US, 19,541 in the low-fat group [2].
- Sources
- [1], [2]
- Caveats
- Heterogeneity was high, and the review explains it by the size of the fat reduction and baseline BMI [1]. The women's trial also raised vegetables, fruit and grains, so fat was not the only change [2].
LDL cholesterol
Shown to lower LDL cholesterol slightly more than higher-fat and low-carbohydrate diets, by about 0.07 to 0.16 mmol/L.
Compared with diets with more fat
The numbers and sources
- Effect
- Against higher-fat diets in people not trying to lose weight, LDL fell 0.13 mmol/L (95% CI 0.05 to 0.21) and total cholesterol 0.23 mmol/L [1]. Against low-carbohydrate diets, LDL was lower on low-fat diets by 0.16 mmol/L (95% CI 0.003 to 0.33) [4], by 0.07 mmol/L at 6 to 12 months (95% CI 0.02 to 0.12) [5] and by 0.14 mmol/L at 6 months (95% CI 0.03 to 0.26) [8]. In postmenopausal women, LDL fell 3.55 mg/dL more than in the comparison group [9].
- Population
- Adults in the trials above [1][4][5]; 447 adults with BMI 25 or more in 5 trials [8]; 48,835 postmenopausal women [9].
- Sources
- [1], [4], [5], [8], [9]
- Caveats
- The differences are about 0.1 mmol/L, or about 4 mg/dL. In [8], the low-fat diets restricted energy and the low-carbohydrate diets did not. LDL is a risk marker, not a heart event.
Mixed results2
Breast cancer
One large trial found no significant change in invasive breast cancer over 8.1 years, and fewer deaths after breast cancer over about 20 years of follow-up.
Compared with diets with more fat
The numbers and sources
- Effect
- Invasive breast cancer occurred in 655 women in the low-fat group (0.42% a year) and 1,072 in the comparison group (0.45%), HR 0.91 (95% CI 0.83 to 1.01) [13]. Over a median of 19.6 years, breast cancer followed by death was lower (HR 0.84, 95% CI 0.74 to 0.96), while invasive breast cancer and colorectal cancer did not differ [14].
- Population
- 48,835 postmenopausal women without prior breast cancer [13][14].
- Sources
- [13], [14]
- Caveats
- The primary result was not significant. The finding on deaths comes from additional analyses of long-term follow-up [14].
- Why limited
- This rests on one trial, of 48,835 people. Strength counts independent studies that agree, so one trial is limited at any size.
Diabetes
One large trial found no change in treated diabetes over 8.1 years, and slightly less diabetes needing insulin over about 20 years of follow-up.
Compared with diets with more fat
The numbers and sources
- Effect
- Treated diabetes was reported by 7.1% of the low-fat group and 7.4% of the comparison group (HR 0.96, 95% CI 0.90 to 1.03) [15]. Over a median of 19.6 years, diabetes requiring insulin was lower (HR 0.87, 95% CI 0.77 to 0.98) [14].
- Population
- 48,835 generally healthy postmenopausal women [14][15].
- Sources
- [14], [15]
- Caveats
- Diabetes was self-reported. The authors write that weight loss, more than macronutrient mix, may be the main predictor of diabetes risk [15].
- Why limited
- This rests on one trial, of 48,835 people. Strength counts independent studies that agree, so one trial is limited at any size.
Not shown to help3
Weight loss against low-carbohydrate and other diets
Shown to produce about 1 to 2 kg less weight loss than low-carbohydrate diets in adults with overweight, and similar loss to other higher-fat diets of equal intensity.
Compared with low-carbohydrate diets, other higher-fat weight-loss diets and usual diet [3]; low-carbohydrate diets [4], [5]; no diet, and low-carbohydrate diets in the same network meta-analysis [6]; a healthy low-carbohydrate diet [7]
The numbers and sources
- Effect
- In weight-loss trials of a year or more, low-carbohydrate diets lowered weight 1.15 kg more than low-fat diets (95% CI 0.52 to 1.79, 18 comparisons, I² 10%). Low-fat diets did not differ from other higher-fat weight-loss diets (0.36 kg, 95% CI -0.66 to 1.37) and lost 5.41 kg more than usual diet [3]. In 11 RCTs lasting 6 months or more, weight fell 2.17 kg more on low-carbohydrate diets (95% CI 0.99 to 3.36) [4]. In 38 studies, the difference at 6 to 12 months was 1.30 kg (95% CI 0.57 to 2.02) [5]. Against no diet, low-fat diets lowered weight 7.99 kg at 6 months and 7.27 kg at 12 months, and low-carbohydrate diets 8.73 kg and 7.25 kg [6]. In a 12-month trial, weight fell 5.3 kg on a low-fat diet and 6.0 kg on a low-carbohydrate diet, a difference of 0.7 kg (95% CI -0.2 to 1.6) [7].
- Population
- 53 trials with 68,128 participants [3]; 1,369 previously healthy adults in 11 RCTs [4]; 6,499 adults in 38 studies [5]; 7,286 adults with overweight or obesity in 48 trials [6]; 609 adults aged 18 to 50 without diabetes, BMI 28 to 40 [7].
- Sources
- [3], [4], [5], [6], [7]
- Caveats
- Low-fat diets led to more loss only against usual diet, so the intensity of the comparison group drives the result [3]. The difference between diet types is small next to the loss on either diet [6]. In the 12-month trial, neither genotype pattern nor insulin secretion predicted who lost more on which diet [7].
Heart attack and stroke against usual diet
One large trial in postmenopausal women found no change in coronary heart disease, stroke or total cardiovascular disease over 8.1 years against usual diet.
Compared with diets with more fat
The numbers and sources
- Effect
- Over a mean of 8.1 years, coronary heart disease (HR 0.97, 95% CI 0.90 to 1.06), stroke (HR 1.02, 95% CI 0.90 to 1.15) and total cardiovascular disease (HR 0.98, 95% CI 0.92 to 1.05) did not differ from the comparison group. By year 6, fat intake was 8.2% of energy lower in the low-fat group [9]. With follow-up through 2010, incidence still did not differ between groups [10].
- Population
- 48,835 postmenopausal women aged 50 to 79 at 40 US centers [9][10].
- Sources
- [9], [10]
- Caveats
- Women only. The fat reduction reached was smaller than the 20% of energy target. Subgroup results differed by heart disease and blood pressure at entry (see Risks) [10].
- Why limited
- This rests on one trial, of 48,835 people. Strength counts independent studies that agree, so one trial is limited at any size.
Heart events against a Mediterranean diet
Shown to have more major heart events than a Mediterranean diet in two trials, one in people with heart disease and one in people at high heart risk.
Compared with diets with more fat
The numbers and sources
- Effect
- In people with coronary heart disease followed for 7 years, major cardiovascular events occurred in 111 of 500 on the low-fat diet and 87 of 502 on the Mediterranean diet, with adjusted hazard ratios of 0.719 to 0.753 for the Mediterranean diet. The difference appeared in men and not in the 175 women [11]. In people at high cardiovascular risk followed for a median of 4.8 years, events occurred in 4.4% of the reduced-fat control group against 3.8% and 3.4% on Mediterranean diets with olive oil or nuts (HR 0.69 and 0.72) [12].
- Population
- 1,002 adults aged 20 to 75 with coronary heart disease in Spain, 82.5% men [11]; 7,447 adults aged 55 to 80 at high cardiovascular risk without cardiovascular disease, 57% women, in Spain [12].
- Sources
- [11], [12]
- Caveats
- Participants knew their diet [11]. In [12], the control group was given advice to reduce fat, and the results were republished after randomization problems were found at some sites. Both trials were in Spain.
How trials defined it
The Women's Health Initiative trial aimed to lower fat from about 35% to 20% of energy and raise vegetables and fruit to 5 servings a day and grains to 6, through group and individual sessions, with no weight or calorie goals. Over the intervention, fat was 8% to 10% of energy lower and carbohydrate 8% to 10% higher than in the comparison group [2][14]. In DIETFITS, 22 group sessions over 12 months aimed for the lowest fat intake people could keep up while emphasizing diet quality, and the low-fat group ate 48% of energy from carbohydrate, 29% from fat and 21% from protein [7]. The Cochrane review included trials of at least 6 months comparing lower with higher fat intake without a weight-loss aim [1]. In the high-risk Mediterranean trial, the control group was given advice to reduce dietary fat [12].
Risks
Reported risks2
Triglycerides and HDL against low-carbohydrate diets
Shown to lower triglycerides less and raise HDL less than low-carbohydrate diets, in three meta-analyses of adults.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Against low-carbohydrate diets, triglycerides were 0.26 mmol/L higher (95% CI 0.15 to 0.37) and HDL 0.14 mmol/L lower (95% CI 0.09 to 0.19) on low-fat diets [4]. At 6 to 12 months the differences were 0.10 mmol/L for triglycerides and 0.05 mmol/L for HDL [5]. At 6 months they were 0.25 mmol/L and 0.12 mmol/L [8].
- Population
- Adults in randomized trials lasting 6 months or more [4][5][8].
- Sources
- [1], [4], [5], [8]
- Caveats
- These differences are relative to low-carbohydrate diets. Against usual higher-fat diets, triglycerides (0.01 mmol/L) and HDL (-0.02 mmol/L) showed little or no difference [1].
Ischemic stroke and heart disease in subgroups
One large trial found more ischemic stroke in healthy women with normal blood pressure, and more coronary heart disease in women who had heart disease at entry.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In women without prior cardiovascular disease and with normal blood pressure, coronary heart disease fell (HR 0.70, 95% CI 0.56 to 0.87), partly offset by a rise in ischemic stroke. In the 3.4% with cardiovascular disease at entry, coronary heart disease was higher, HR 1.47 (95% CI 1.12 to 1.93) during the intervention and 1.61 (95% CI 1.02 to 2.55) after it [10].
- Population
- 48,835 postmenopausal women aged 50 to 79 [10].
- Sources
- [10]
- Caveats
- Subgroup analyses. The abstract gives no figure for the stroke rise. The authors cite evidence that results in women with heart disease or high blood pressure at entry are confounded by cholesterol-lowering drug use after randomization [10].
- Why limited
- This rests on one trial, of 48,835 people. Strength counts independent studies that agree, so one trial is limited at any size.
Claims tested and not found
- That a low-fat, higher-carbohydrate diet causes weight gain. Postmenopausal women on a low-fat pattern stayed lighter than controls over 7.5 years, with no tendency to gain by age, ethnicity or BMI [2].
- That a low-fat diet prevents heart disease in older women. Coronary heart disease, stroke and total cardiovascular disease did not differ from usual diet over 8.1 years [9].
- That genotype or insulin secretion predicts who does better on a low-fat diet. Neither interacted with diet type in a 609-person, 12-month trial [7].
Sources
- Hooper L, Abdelhamid AS, Jimoh OF, et al. Effects of total fat intake on body fatness in adults. Cochrane Database of Systematic Reviews. 2020. https://doi.org/10.1002/14651858.cd013636
- Howard BV, Manson JE, Stefanick ML, et al. Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial. JAMA. 2006. https://doi.org/10.1001/jama.295.1.39
- Tobias DK, Chen M, Manson JE, et al. Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis. The Lancet Diabetes & Endocrinology. 2015. https://doi.org/10.1016/s2213-8587(15)00367-8
- Mansoor N, Vinknes KJ, Veierød MB, et al. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. British Journal of Nutrition. 2015. https://doi.org/10.1017/s0007114515004699
- Chawla S, Tessarolo Silva F, Amaral Medeiros S, et al. The Effect of Low-Fat and Low-Carbohydrate Diets on Weight Loss and Lipid Levels: A Systematic Review and Meta-Analysis. Nutrients. 2020. https://doi.org/10.3390/nu12123774
- Johnston BC, Kanters S, Bandayrel K, et al. Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis. JAMA. 2014. https://doi.org/10.1001/jama.2014.10397
- Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial. JAMA. 2018. https://doi.org/10.1001/jama.2018.0245
- Nordmann AJ, Nordmann A, Briel M, et al. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Archives of Internal Medicine. 2006. https://doi.org/10.1001/archinte.166.3.285
- Howard BV, Van Horn L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006. https://doi.org/10.1001/jama.295.6.655
- Prentice RL, Aragaki AK, Van Horn L, et al. Low-fat dietary pattern and cardiovascular disease: results from the Women's Health Initiative randomized controlled trial. The American Journal of Clinical Nutrition. 2017. https://doi.org/10.3945/ajcn.117.153270
- Delgado-Lista J, Alcala-Diaz JF, Torres-Peña JD, et al. Long-term secondary prevention of cardiovascular disease with a Mediterranean diet and a low-fat diet (CORDIOPREV): a randomised controlled trial. The Lancet. 2022. https://doi.org/10.1016/s0140-6736(22)00122-2
- Estruch R, Ros E, Salas-Salvadó J, et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. New England Journal of Medicine. 2018. https://doi.org/10.1056/nejmoa1800389
- Prentice RL, Caan B, Chlebowski RT, et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006. https://doi.org/10.1001/jama.295.6.629
- Prentice RL, Aragaki AK, Howard BV, et al. Low-Fat Dietary Pattern among Postmenopausal Women Influences Long-Term Cancer, Cardiovascular Disease, and Diabetes Outcomes. The Journal of Nutrition. 2019. https://doi.org/10.1093/jn/nxz107
- Tinker LF, Bonds DE, Margolis KL, et al. Low-fat dietary pattern and risk of treated diabetes mellitus in postmenopausal women: the Women's Health Initiative randomized controlled dietary modification trial. Archives of Internal Medicine. 2008. https://doi.org/10.1001/archinte.168.14.1500