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If you want you can skip the explanation and skip straight to the bottom, where I say exactly what I am looking for.

I was talking to my step-dad today and mentioned the recent Oxford study that shows people who do not eat meat have a 14% lower chance of getting cancer.

He suggested it could be because the vegetarians are a certain type of people, who are also less likely to smoke, more likely to exercise, etc. (A fair point, even the study itself mentions this limitation.)

I mentioned that there are many Randomised Controlled Trial studies (which should take care of his previous criticism of vegetarians being generally healthier) where they show that a plant based diet can reverse cardiovascular problems etc.

He said that even in this case, if the plant based diet in the RCT study is simply competing against an average omni diet, then it does not take much to come out ahead, because an average omni diet is full of super unhealthy food like bacon, red meat, cheese, etc. In that case, he argued, the study simply proves that going on a healthy diet is better than eating like an average person, but that you could achieve the same by going on a "healthy" omni diet with lots of fish, poultry, eggs, vegetables, fruits, greens, whole grains, etc.

What I am looking for:

So, both him and I agree, that the absolute best study would be one that satisfies the following criteria:

  1. Randomized controlled trial study

  2. A test group on a plant-based diet

  3. A control group on a "healthy" omnivore diet. By "healthy" I mean the kind of diet than mainstream non-plant-based nutritionists and dieticians recommend. For example, based on whole grains, fish, vegetables, fruits leafy greens, and white meat. It does not need to be exactly that, it just need to be what most people would associate with "healthy".

  4. The study could look at anything related to health, but preferably to avoiding or reversing serious illnesses or risk factors. I realize an RCT looking at prevention of illnesses is unlikely to exist, but I am hoping at least one on reversing may exist.

Does a study satisfying these criteria exist?

If not, what is the most credible research I could point to? Maybe like a comprehensive review, meta analysis of many different studies or something.

1
  • 2
    I remember reading that while (statistically) vegetarians are healthier than omnivores in countries like the UK and US, in India vegetarians are not healthier than non-vegetarians
    – Zanna
    Mar 1, 2022 at 7:50

1 Answer 1

3

Adventists Health Study 2

The study explores the links between lifestyle, diet and disease among Seventh-day Adventists.
It started in 2001 and is still ongoing.

Why adventists ?

Seventh-day Adventists have a lower risk than other Americans of certain diseases, and many researchers hypothesize that this is due to dietary and other lifestyle habits. We know this thanks to the previous Adventist Health Studies. (1)

Characteristics of the participants

- Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
Prevalence
(%)
7.7 29.2 9.9 5.4 47.7
All meats, including fish
(servings)
<1/mo <1/mo ≥1/mo ≥1/mo but ≤1/wk >1/wk
Nonfish meat
(servings)
<1/mo <1/mo <1/mo ≥1/mo but ≤1/wk ≥1/mo
Fish
(servings)
<1/mo <1/mo ≥1/mo ≤1/wk Any amount
Eggs and dairy products
(servings)
<1/mo ≥1/mo Any amount Any amount Any amount
Age
(y)
57.9 ± 13.6 57.5 ± 13.9 58.8 ± 13.7 57.8 ± 14.1 55.9 ± 13.1
Female sex
(%)
63.8 64.9 68.0 69.7 65.3
Race, black
(%)
21.0 13.6 39.1 17.8 34.0
Marital status, married
(%)
75.6 76.3 73.1 71.5 70.3
Educational level (%) Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
High school or less 16.7 13.9 18.4 21.3 24.4
 Trade, associate, some college 39.4 35.7 38.1 39.2 42.2
 Bachelor’s degree 24.4 25.3 23.0 21.3 19.2
 Graduate degree 19.5 25.1 20.5 18.3 14.1
Alcohol consumption (%) Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
 None 98.8 96.8 92.5 92.4 83.4
 Rare 0.6 1.8 4.0 4.2 7.5
 Monthly 0.2 0.5 1.1 1.1 3.1
 Weekly 0.3 0.7 1.9 2.0 4.7
 Daily 0.1 0.2 0.5 0.3 1.3
Smoking (%) Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
 Never 85.0 88.2 84.1 81.4 75.7
 Former 14.9 11.7 15.5 18.3 22.3
 Current 0.1 0.1 0.4 0.3 2.0
Exercise (%) Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
 None 15.1 17.3 18.0 20.6 23.4
 1–20 min/wk 16.2 18.6 16.8 20.5 20.0
 21–60 min/wk 16.1 16.5 16.2 16.1 15.8
 61–150 min/wk 27.8 26.8 27.5 24.5 23.6
 ≥151 min/wk 24.8 20.8 21.6 18.3 17.2
Nutrients Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
 Carbohydrate
(%)
58.1 ± 0.1 54.3 ± 0.1 54.5 ± 0.1 53.9 ± 0.1 51.4 ± <0.1
 Fat
(%)
28.2 ± 0.1 31.9 ± 0.1 31.3 ± 0.1 32.2 ± 0.1 33.8 ± <0.1
 Protein
(%)
13.6 ± <0.1 13.7 ± <0.1 14.2 ± <0.1 13.7 ± <0.1 14.7 ± <0.1
 Total fiber
(g/d)
46.7 ± 0.1 37.5 ± 0.1 37.7 ± 0.1 34.9 ± 0.1 30.4 ± <0.1
 SFAs
(g/d)
11.6 ± 0.1 16.0 ± 0.1 15.8 ± 0.1 17.4 ± 0.1 19.9 ± <0.1
 Animal protein
(g/d)
3.1 ± 0.2 12.2 ± 0.1 16.0 ± 0.2 17.6 ± 0.2 31.8 ± 0.1
Energy intake
(kcal/d)
1897 ± 729 1912 ± 735 1939 ± 772 1720 ± 713 1884 ± 773

Findings

These studies showed the advantage of a vegetarian and vegan diet among Adventists, found strong evidence that meat increased risk of colon cancer and coronary heart disease, and that nut consumption reduced risk of coronary heart disease. Other significant associations between cancers and other foods have also been reported. (2)

Cross-sectional findings Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
BMI2
(kg/m2)
23.6 ± 4.4 25.7 ± 5.1 26.3 ± 5.2 27.3 ± 5.7 28.8 ± 6.3
 Diabetes
[OR (95% CI)]
0.51
(0.40, 0.66)
0.54
(0.49, 0.60)
0.70
(0.61, 0.80)
0.76
(0.61, 0.80)
Referent
 Prevalence
(%)
2.9 3.2 4.8 6.1 7.6
 Hypertension
(Nonblacks)
[OR (95% CI)]
0.37
(0.19, 0.74)
0.57
(0.36, 0.92)
0.92
(0.70, 1.50)
- Referent
 Hypertension
(Blacks)
[OR (95% CI)]
0.56
(0.36, 0.87)
- 0.94
(0.54, 1.63)
Not reported Referent
 Metabolic syndrome
[OR (95% CI)]
0.44
(0.30, 0.64)
- Not reported - Referent
 Prevalence
(%)
25.2 - 37.6 - 39.7
Prospective findings Vegan Lactoovovegetarian Pescovegetarian Semivegetarian Nonvegetarian
 Diabetes
[OR (95% CI)]
0.38
(0.24, 0.62)
0.62
(0.50, 0.76)
0.79
(0.58, 1.09)
0.49
(0.31, 0.76)
Referent
n 3545 14,099 3644 2404 17,695
 Incident cases
(%)
0.54 1.08 1.29 0.92 2.12
 All cancers
[HR (95% CI)]
0.84
(0.72, 0.99)
0.93
(0.85, 1.02)
0.88
(0.77, 1.01)
0.98
(0.82, 1.17)
Referent
n 4922 19,735 6846 3881 33,736
 No. of events 190 878 276 182 1413
 All-cause mortality
[HR (95% CI)]
0.85
(0.73, 1.01)
0.91
(0.82, 1.00)
0.81
(0.69, 0.94)
0.92
(0.75, 1.13)
Referent
n 5548 21,777 7194 4031 35,359
 No. of events 197 815 251 160 1147

(1) https://en.wikipedia.org/wiki/Adventist_Health_Studies#
(2) https://academic.oup.com/ajcn/article/100/suppl_1/353S/4576455?login=false

That's the closest i've got at the moment.
You might want to look at the study/studies (?) Dr Neal Barnard mentions that led him to use a plant based diet to reverse type 2 diabetes but I doubt they'd meet your criteria.

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