The BROAD study randomized 65 people ages 35-70 to either a control group (n=32) or a whole foods plant-based (WFPB) diet with supplemental vitamin B12 group (n=33). This WFPB diet was starch-based and the B12 supplement was methycolbalamin, not the common cyanocobalamin:
"This dietary approach included whole grains, legumes, vegetables and fruits. Participants were advised to eat until satiation. We placed no restriction on total energy intake. Participants were asked to not count calories. We provided a ‘traffic-light’ diet chart to participants outlining which foods to consume, limit or avoid (Supplementary Table S1). We encouraged starches such as potatoes, sweet potato, bread, cereals and pasta to satisfy the appetite. Participants were asked to avoid refined oils (e.g. olive or coconut oil) and animal products (meat, fish, eggs and dairy products). We discouraged high-fat plant foods such as nuts and avocados, and highly processed foods. We encouraged participants to minimise sugar, salt and caffeinated beverages. We provided 50 μg daily vitamin B12 (methylcobalamin) supplements. The intervention group attended 2-h evening sessions twice-weekly for 12 weeks. We ran sessions at a local polytechnic, incorporating a chef-guided cooking tutorial and presentation by doctors, with a discussion. Programme outline provided (Supplementary Table S2). Special events included screening the documentary 'Forks Over Knives' and an accompanying film endorsing the WFPB diet; discussion sessions; restaurant meals; quiz night; potlucks; and graduation ceremony. Both intervention and control group participants received $40 petrol vouchers to cover travel costs and received a birthday card along with a voucher redeemable for a native plant."The control group received only "standard medical care" which is not described in detail in the report, but there is no mention of the 'standard' group receiving any dietary guidance at all. It seems likely that the intervention group received much more interaction with health care providers and had strong social support to adhere to the WFPB diet.
The results were impressive to some WFPB diet advocates, but not so much in my view.
Mean BMI reduction was 4.4 at 6 months, but only 4.2 at 12 months; this means that over the second 6 months, some people regained weight lost in the first 6 months. In the authors' words "From 6 to 12 months intervention BMI increased non-significantly by 0.4."
Mean weight reduction at 6 months was 12.1 kg, and at 12 months was 11.5 kg. Again, people lost weight during the first six months, then some regained. More importantly to me, no data is given on the nature of the weight loss. What proportion was fat or lean? No data provided.
Cholesterol reduction followed a similar pattern. "Within the intervention group mean reduction in total cholesterol was statistically significant at all time periods, although there was a smaller effect size with time: at month 3 it was 0.95 mmol l−1; at month 6 it was 0.71 mmol l−1; and at month 12 it was 0.55..."
In the BROAD study, the mean baseline body weight and BMI of subjects eating the WFPB diet were, respectively, 94.8 kg and 34.5, and these declined to 82.9 kg and 30.2 at 6 months. For comparison, in the Jonsson et al. study using a paleolithic diet intervention in 13 subjects with T2 diabetes, the mean baseline body weight and BMI of subjects eating the paleolithic diet were, respectively, 87 kg and 30, and these declined to 82 kg and 28. Thus the subjects eating the WFPB diet had a mean weight loss of 12.1 kg over 6 months, while the subjects eating the paleolithic diet had a mean weight loss of 5 kg over 6 months. It is worth noting however the the subjects in the BROAD study started 7 kg heavier than those in the paleolithic diet study; generally, the rate of initial weight loss is greater the higher the initial starting weight. Also, weight loss essentially stopped after 6 months in the BROAD study, and we don't know what happened after 6 months in the Jonsson et al. study. Achieving a healthy body weight is a long-term proposition and this study doesn't inspire confidence that the WFPB diet is particularly successful long-term, since those eating the WFPB diet did not lose weight between 6 and 12 months and were still on average in the obese category at the 12 month mark.
As I will discuss below, adherence to the WFPB diet deteriorated significantly over the 12 months of follow-up. I will also add that when first adopting a WFPB diet many people do not understand how much whole plant food one must eat to achieve a normal caloric intake. In my experience, most people new to a WFPB diet take portions similar to what they are used to eating of foods having a higher energy density. After some time with the diet, people get the idea and get really hungry, and find that they are able to eat large amounts of starches. This might account for a stalling of weight loss as participants became more familiar with the WFPB diet.
In the BROAD intervention group the mean total cholesterol decreased from 5.4 mmol l−1 (208 mg/dL) at baseline to 4.5 (174) at 3 months, then rose to 4.7 (182) at 6 months, and to 5.0 (193) at 12 months. For comparison, in the Jonsson et al. paleolithic diet study the mean cholesterol in that trial started at 4.4 mmol (170 mg/dL) and consistently dropped to 4.3 (166 mg/dL) at 6 months during which time the subjects consumed a mean of 340 g (~0.62 lb.) meat, meat products, and fish and 71 g eggs (about 1.5 eggs) every day and had a mean daily intake of 577 mg cholesterol.
The apparent paradox here is that the subjects eating the meat- and cholesterol-rich paleolithic diet and having a slightly slower rate of weight loss had a more consistent trend to lower total cholesterol levels, and achieved lower total cholesterol levels at 6 months, than subjects eating the WFPB diet in the BROAD project.
According to the BROAD report, HDL decreased slightly (baseline 1.3, 3 months 1.1, 6 months 1.2) in subjects on the WFPB diet, despite total cholesterol reduction being rather modest and short-lived. In contrast, in the paleolithic diet study by Jonsson et al. HDL remained stable over 6 months despite a consistent reduction in total cholesterol.
According to the BROAD report the cholesterol reduction at 6 months was not significantly different from the control group : "Comparing standard care plus dietary programme (intervention) to standard care (control) at month 6, our analysis showed a nonsignificant reduction in total cholesterol at 0.45."
How did this happen? The control group was taking cholesterol-lowering medications. In fact, "Control group medications increased from 74 to 80 over 6 months, an 8% increase, and intervention group medication usage decreased from 94 to 74 at 6 months, and to 67 over 12 months: a 29% decrease..." So, a positive interpretation is that the WFPB diet produced cholesterol reductions similar to pharmaceutical treatments.
In the BROAD study, triglycerides increased in subjects eating the WFPB diet, starting at 1.6 at baseline, up to 1.8 at 3 months and 1.9 at 6 months. In the Jonsson et al. paleolithic diet study, triglycerides declined from 1.5 at baseline to 1.3 at 3 months and 1.2 at 6 months. Comparing these two studies, the paleolithic diet appears more effective than a starch-based WFPB diet at reducing triglycerides.
The authors of the BROAD study describe the intervention participants as "highly adherent with the dietary changes, although this decreased with time." They report that "Multiple intervention participants stated 'not being hungry' was important in enabling adherence."
Nevertheless, despite reporting 'not being hungry' and getting intensive education and social support, adherence to the WFPB diet declined significantly over time: "Dietary indiscretions (diet) over 3 days were used as adherence measure...In the intervention group, indiscretions increased significantly from 1 at 3 months to 3 (±1) at 6 months, and then increased significantly to 5 (±1) at 1 year." Assuming 3 meals daily, 5 'indiscretions' over 3 days suggests an 'indiscretion' at more than half of meals by 12 months.
I am curious to know whether these 'indiscretions' consisted more of refined plant foods, higher fat plant foods, or animal products but the authors of the BROAD report give no data in this report. In contrast Jonsson et al. listed in their Table 5 the mean intakes of beans, cereals, rice, milk products, bakery products by their subjects when assigned to the paleolithic diet intervention. It appears that the subjects assigned to the paleolithic diet intervention were able to reduce intakes of these items to negligible levels for 6 months.
In the BROAD study, HbA1c (mmolmol-1) declined in the WFPB intervention group from 42 (6%) to 39 (5.7%) at 6 months and to 37 (5.5%) at 12 months. Thus, over 6 months the decline (using HbA1c%) was 5%. In comparison, Jonsson et al. reported a decline of HbA1c from 6.6% to 5.6% over 6 months, or 15% in subjects consuming a paleolithic diet. Comparing these two studies alone, the paleolithic diet appears to have been far more effective in reducing HbA1c levels.
According to Table 2 of the BROAD report, both systolic and diastolic blood pressure were virtually unchanged over 6 months of WFPB diet (baseline 133/81, 6 months 132/82). In comparison, Jonsson et al. reported a baseline mean BP of 150/83 and a decline to 145/82 at 6 months in their paleolithic diet intervention.
The BROAD report does not include data on C-reactive protein (CRP), a measure of systemic inflammation. I would have liked to see this, given that systemic inflammation is a risk factor for cardiovascular disease. Jonsson et al. reported a decrease in CRP from 2.4 at baseline to 1.8 at 6 months for their subjects consuming a paleolithic diet. It would be interesting to know if the WFPB diet matched or surpassed this.
Of particular interest in comparing these studies is the difference in amount of educational time devoted to helping the subjects adopt the intervention diets. As already quoted above, in the BROAD study subjects received quite a bit of education, documentaries, support groups, restaurant meals, potlucks, etc.. In comparison, in the paleolithic diet intervention study of Jonsson et al. the instruction was quite limited, as described in their report:
"All eligible subjects were informed of the intention to compare two healthy diets in the treatment of type 2 diabetes and that it was unknown if any of them would be superior to the other. At study start all eligible subjects were randomized to start with either a Diabetes diet in accordance with current guidelines  or a Paleolithic diet. Randomization was performed by UCB, GP and AH by opening opaque, sealed envelopes (prepared by TJ) containing a note of the initial diet with equal proportions of envelopes for both diets. After randomization, there was no blinding of dietary assignment to study participants, nor to those administering the interventions or assessing the outcomes. Immediately after randomization, all subjects received oral and written information individually (by UCB, GP or AH) in the morning about their respective initial diet. After three months all subjects switched diets and received new oral and written information individually (by UCB, GP or AH) about the diet of the following three months. Written information with dietary advice and food recipes were similarly formulated for both diets. For increased conformity, the dietary advice and data collection procedure were discussed by all authors except YG at several meetings prior to start of study. Advice about regular physical activity was given equally to all subjects.
"The information on the Diabetes diet stated that it should aim at evenly distributed meals with increased intake of vegetables, root vegetables, dietary fiber, whole-grain bread and other whole-grain cereal products, fruits and berries, and decreased intake of total fat with more unsaturated fat. The majority of dietary energy should come from carbohydrates from foods naturally rich in carbohydrate and dietary fiber. The concepts of glycemic index and varied meals through meal planning by the Plate Model were explained . Salt intake was recommended to be kept below 6 g per day.
In both the BROAD study and the Jonsson et al. study subjects were allowed to consume some foods in unlimited quantities (WFPB: whole grains, legumes, vegetables, fruits; Paleolithic diet: lean meat, fish, fruit, leafy and cruciferous vegetables, root vegetables). In both studies subjects lost body weight without intentional energy restriction. However, in the Jonsson et al. the outcomes were achieved without giving the subjects support groups, cooking classes, potlucks and so on. In the BROAD study the greatest beneficial changes occurred in the first three months, during which the subjects received the intensive intervention with twice weekly meetings, cooking classes, potlucks, documentary viewings, and so on. After 3 months adherence declined and some markers started to reverse. This might suggest that people can adhere to a low-fat, starch-based WFPB diet only when intensively coached and supported; while it seems the subjects assigned to the paleolithic diet in the study by Jonsson et al. were able to adopt and adhere to a paleolithic diet without similarly intensive intervention and yet achieve progressive improvements in metabolic function."The information on the Paleolithic diet stated that it should be based on lean meat, fish, fruit, leafy and cruciferous vegetables, root vegetables, eggs and nuts, while excluding dairy products, cereal grains, beans, refined fats, sugar, candy, soft drinks, beer and extra addition of salt. The following items were recommended in limited amounts for the Paleolithic diet: eggs (≤2 per day), nuts (preferentially walnuts), dried fruit, potatoes (≤1 medium-sized per day), rapeseed or olive oil (≤1 tablespoon per day), wine (≤1 glass per day). The intake of other foods was not restricted and no advice was given with regard to proportions of food categories (e.g. animal versus plant foods). The evolutionary rationale for a Paleolithic diet and potential benefits were explained ."
The authors of the BROAD study attributed the weight loss in subjects eating the WFPB diet to a reduction in energy density of the diet.
"This randomised controlled trial compared a 12-week WFPB dietary programme to normal care alone. The intervention led to significant and sustained BMI and weight reduction at all measurement points compared with the control group. To the best of our knowledge, there are no randomised controlled trials that have achieved a greater average weight loss over a 6- or 12-month period, without mandating regular exercise or restricting total caloric intake.9, 10, 41 The key difference between this trial and other approaches to weight loss was that participants were informed to eat the WFPB diet ad libitum and to focus efforts on diet, rather than increasing exercise. The mechanism for this is likely the reduction in the energy density of the food consumed (lower fat, higher water and fibre).42"Unfortunately it appears that this reduction of energy density was efficacious for only a limited time. In contrast, Jonsson et al. offer several lines of explanation for the effectiveness of the paleolithic diet intervention; in their words:
"No advice was given to restrict food intake. Therefore, the lower reported energy intake during the Paleolithic diet despite no difference in weight of reported food intake agrees with the notion that such a diet is satiating and facilitates a reduced caloric intake [4,27]. Accordingly, energy density was lower in the Paleolithic diet and also correlated with alterations of both weight and waist circumference. The higher amount of fruit and vegetables during the Paleolithic period may have promoted weight loss due to its high content of water, which is thought to be satiating . Interestingly, the Paleolithic diet appeared to be satiating despite a lower content of fiber in this study. The slightly higher relative protein intake, as percentage of total calorie intake, may also have added to a satiating effect [29,30]. Alternative explanations on satiation, such as dietary effects on leptin resistance, could also be considered ."
"A reduced energy intake would evidently be a major explanation for the beneficial effects of the Paleolithic diet on weight and waist circumference. Meta-analyses and large trials with various lifestyle interventions indicate that reduced caloric intake is more important for long-term weight loss than other known dietary factors, including macronutrient composition [32-40]. In studies shorter than 6 months, such as this one, differences in GI and/or GL may also have played a role for weight change. A Cochrane review found that overweight or obese people lost slightly more weight during 5–12 weeks of low GI diets , and short-term carbohydrate restriction possibly results in greater weight loss than low-fat diets . However, dietary GI and dietary GL did not correlate with alterations of weight, waist circumference or metabolic variables in our study. It should also be noted that, in the present study, reported mean absolute carbohydrate intake in the Paleolithic diet (g per day) was only slightly below the 130 g per day recommended by the American Diabetes Association, and clearly above 50 g per day, which has been proposed as the level below which a diet should be termed a low carbohydrate diet ."All in all, the BROAD study results were not as exceptional as advocates of whole foods plant-based diets might like them to be. Although the initial weight loss was large, it was not sustained for more than 6 months, and adherence deteriorated substantially after 3 months despite intensive initial intervention. It also appears that the WFPB diet did not have uniquely favorable effects on total cholesterol. It appeared less effective than a paleolithic diet for reducing HbA1c and blood pressure, and actually increased triglycerides despite being composed of unrefined starches, whereas a paleolithic diet intervention decreased triglycerides. I feel disappointed that the BROAD study authors either did not measure or did not report CRP levels, so we don't know if it performs as well as or better than a paleolithic diet intervention in this respect.