Flexitarian diet
Research on flexitarian or semi-vegetarian eating is thin. One small trial found weight loss matched an omnivorous diet. In a large Adventist cohort, semi-vegetarians had less diabetes, while death, colorectal cancer and hypertension rates did not differ significantly from nonvegetarians. No study measured heart disease directly, and no harms or nutrient shortfalls were sourced.
- Status
- A dietary pattern, not a regulated product.
- Also called
- semi-vegetarian diet, semivegetarian, flexible vegetarian, part-time vegetarian, reducetarian, mostly plant-based
- Followed for
- weight loss, diabetes prevention, blood pressure, heart health, cancer prevention, longevity, gut health, Crohn's disease
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 help3
- LimitedLinked to lower diabetes prevalence and incidence in semi-vegetarians than nonvegetarians in one large Adventist cohort.
- LimitedOne small uncontrolled study found 15 of 16 people with Crohn's disease who kept a semi-vegetarian diet stayed in remission over the 2-year study.
- LimitedLimited evidence: in a review of 4 trials in healthy adults, replacing part of animal protein with plant protein lowered LDL and total cholesterol. No study measured heart disease itself.
Reported risks0
No risks sourced yet.
What people follow it for, and what was found
Shown to help3
Type 2 diabetes
Linked to lower diabetes prevalence and incidence in semi-vegetarians than nonvegetarians in one large Adventist cohort.
Compared with nonvegetarian Seventh-day Adventists in the US and Canada [1], [2]
The numbers and sources
- Effect
- Diabetes prevalence was 6.1% in semi-vegetarians against 7.6% in nonvegetarians (adjusted OR 0.76, 95% CI 0.65 to 0.90) [1]. Over two years, new diabetes developed in 0.92% of semi-vegetarians and 2.12% of nonvegetarians (adjusted OR 0.486, 95% CI 0.312 to 0.755) [2].
- Population
- 60,903 Seventh-day Adventist church members in North America [1]; 41,387 members free of diabetes at baseline [2]. Observational.
- Sources
- [1], [2]
- Caveats
- Observational, one cohort, self-reported diabetes. Both analyses adjusted for BMI and lifestyle, and associations grew stronger without BMI adjustment [2]. Among Black participants, the semi-vegetarian link was not reported as significant [2].
Crohn's disease relapse
One small uncontrolled study found 15 of 16 people with Crohn's disease who kept a semi-vegetarian diet stayed in remission over the 2-year study.
Compared with patients who chose not to continue the diet and ate an omnivorous diet [8]
The numbers and sources
- Effect
- Remission held in 15 of 16 patients who continued the diet (94%) against 2 of 6 who returned to an omnivorous diet (33%) over 2 years (log-rank P = 0.0003) [8].
- Population
- 22 adults with Crohn's disease in remission at a single center [8].
- Sources
- [8]
- Caveats
- Not randomized. Patients chose whether to continue the diet, and the comparison group had 6 people [8].
Heart disease
Limited evidence: in a review of 4 trials in healthy adults, replacing part of animal protein with plant protein lowered LDL and total cholesterol. No study measured heart disease itself.
Compared with diets with a higher share of animal protein foods [9]
The numbers and sources
- Effect
- A 2026 systematic review found 4 dietary interventions, reported in 7 articles, that partially replaced animal protein foods with plant protein foods in healthy adults. LDL cholesterol, total cholesterol and body weight improved in those eating the higher share of plant protein. Vitamin B12 status fell on the diets with the most plant protein [9].
- Population
- Healthy adults with a mean or median age of 18 to 65 in randomized trials, 3 of 7 articles at low risk of bias [9].
- Sources
- [9]
- Caveats
- The abstract gives no pooled sizes of effect [9]. Cholesterol is a risk marker, not heart disease. No cohort or trial of flexitarian eating and heart attacks or heart deaths was located.
Mixed results1
Weight
One small trial found weight loss on a semi-vegetarian diet matched an omnivorous diet over 6 months. A large cohort linked it to slightly lower BMI.
Compared with nonvegetarian Seventh-day Adventists in North America [1]; an omnivorous diet and a vegan diet, all low-fat and low-glycemic-index, in South Carolina adults [3]
The numbers and sources
- Effect
- In a 6-month trial, weight fell 3.2% on a semi-vegetarian diet and 3.1% on an omnivorous diet, both low-fat and low-glycemic-index, against 7.5% on a vegan diet [3]. In the Adventist cohort, mean BMI was 27.3 in semi-vegetarians and 28.8 in nonvegetarians [1].
- Population
- 63 adults with overweight or obesity, 13 assigned to the semi-vegetarian diet, 79% completed [3]; Adventist adults, observational [1].
- Sources
- [1], [3]
- Caveats
- Very small trial arms. The omnivorous group met monthly while the other groups met weekly for the first 2 months [3]. A 2017 review of 25 studies described the evidence on weight and metabolic health as emerging [4].
Not shown to help3
Blood pressure
Limited evidence: hypertension odds did not differ significantly between partial vegetarians and omnivores in one Adventist cohort sample.
Compared with omnivorous white Adventists in the USA and Canada [5]
The numbers and sources
- Effect
- Against omnivores, the odds of hypertension in partial vegetarians were 0.92 (95% CI 0.50 to 1.70) [5].
- Population
- 500 white participants from a calibration substudy of the Adventist cohort, observational [5].
- Sources
- [5]
- Caveats
- Observational and small. The paper calls the group partial vegetarians [5].
Death from any cause
Limited evidence: death rates did not differ significantly between semi-vegetarians and nonvegetarians over about 6 years in one Adventist cohort.
Compared with nonvegetarian Seventh-day Adventists in North America [6]
The numbers and sources
- Effect
- The adjusted hazard ratio for death from any cause in semi-vegetarians was 0.92 (95% CI 0.75 to 1.13) against nonvegetarians [6].
- Population
- 73,308 Seventh-day Adventists in North America followed a mean 5.79 years, observational [6].
- Sources
- [6]
- Caveats
- Observational, one cohort with a short follow-up [6].
Colorectal cancer
Limited evidence: colorectal cancer rates did not differ significantly between semi-vegetarians and nonvegetarians in one Adventist cohort.
Compared with nonvegetarian Seventh-day Adventists in North America [7]
How trials defined it
Reviews describe a flexitarian or semi-vegetarian diet as mainly vegetarian with occasional meat or fish [4]. The Adventist cohort classified diet type from a food frequency questionnaire [1][6]. The 6-month weight trial used low-fat, low-glycemic-index diets in every arm, with no emphasis on calorie restriction [3]. The Crohn's study advised patients to keep the semi-vegetarian diet served in hospital and avoid foods considered high risk for inflammatory bowel disease [8].
Sources
- Tonstad S, Butler T, Yan R, et al. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care. 2009. https://doi.org/10.2337/dc08-1886
- Tonstad S, Stewart K, Oda K, et al. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2. Nutrition, Metabolism and Cardiovascular Diseases. 2013. https://doi.org/10.1016/j.numecd.2011.07.004
- Turner-McGrievy GM, Davidson CR, Wingard EE, et al. Comparative effectiveness of plant-based diets for weight loss: a randomized controlled trial of five different diets. Nutrition. 2015. https://doi.org/10.1016/j.nut.2014.09.002
- Derbyshire EJ. Flexitarian Diets and Health: A Review of the Evidence-Based Literature. Frontiers in Nutrition. 2017. https://doi.org/10.3389/fnut.2016.00055
- Pettersen BJ, Anousheh R, Fan J, et al. Vegetarian diets and blood pressure among white subjects: results from the Adventist Health Study-2 (AHS-2). Public Health Nutrition. 2012. https://doi.org/10.1017/S1368980011003454
- Orlich MJ, Singh PN, Sabaté J, et al. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA Internal Medicine. 2013. https://doi.org/10.1001/jamainternmed.2013.6473
- Orlich MJ, Singh PN, Sabaté J, et al. Vegetarian dietary patterns and the risk of colorectal cancers. JAMA Internal Medicine. 2015. https://doi.org/10.1001/jamainternmed.2015.59
- Chiba M, Abe T, Tsuda H, et al. Lifestyle-related disease in Crohn's disease: relapse prevention by a semi-vegetarian diet. World Journal of Gastroenterology. 2010. https://doi.org/10.3748/wjg.v16.i20.2484
- Courtney A, Sweeney R, McNulty B, et al. Partially replacing animal-based protein foods with plant-based protein foods: a systematic review of randomized controlled trials in healthy adults. Nutrition Reviews. 2026. https://doi.org/10.1093/nutrit/nuag058