Single-Arm 8-Week Ad Libitum Self-Prepared Paleo Diet Reduces Cardiometabolic Disease Risk Factors in Overweight Adults

Abstract

The paleo diet is popular among the general population due to promoted weight loss and disease prevention benefits. We examined the effectiveness of a self-administered paleo diet in improving cardiometabolic disease risk factors. Overweight, physically inactive but otherwise healthy adults (males = 4, females = 3, age 32.7 ± 4.9 years, body mass index [BMI] 29.4 ± 2.4 kg/m²) habitually eating a traditional Western diet (1853.4 ± 441.2 kcal; 34.0% carbohydrate; 41.4% fat; 19.2% protein) completed an ad libitum self-administered paleo diet for 8 weeks. Height, weight, blood pressure, and a fasting blood sample were collected pre– and post–paleo dietary intervention. Blood samples were analyzed for fasting cardiometabolic disease biomarkers—including brain-derived neurotropic factor (BDNF), fibroblast growth factor (FGF) 21, and leptin. After 8 weeks, body mass (−5.3 kg, P = .008), BMI (−1.7 kg/m², P = .002), serum leptin (−56.2%, P = .012), serum FGF21 (−26.7%, P = .002), and serum BDNF (−25.8%, P = .045) significantly decreased. Systolic and diastolic blood pressure were unchanged following the paleo dietary intervention (P > .05). Average energy intake (−412.6 kcal, P = .016) significantly decreased with the paleo dietary intervention mostly due to a reduction in carbohydrate consumption (−69.2 g; P = .003). An 8-week self-administered paleo dietary intervention was effective in improving cardiometabolic disease risk factors in a healthy, physically inactive overweight adult population.

‘. . . the paleo diet has been a popular Western diet alternative over the past decade.’

Excessive body fat is a significant risk factor for many diseases and conditions, including cardiovascular disease, stroke, and type 2 diabetes. ¹ The Western diet is frequently implicated in promoting the prevalence of cardiometabolic disease–related risk factors,^2-5 and the paleo diet has been a popular Western diet alternative over the past decade. The paleo diet is an eating plan modeled after supposed hunter-gatherer populations; therefore, the dietary guidelines for the paleo diet diverge substantially from modern nutritional guidelines.^6-9 This rift is especially due to the avoidance of grains and dairy products in the paleo diet compared with many other diets that often recommend these foods as beneficial for the cardiovascular system. ¹⁰ It is estimated that people who follow Western diets consume 23.9% of calories form cereal grains, 16.8% from refined sugars, and 10.6% from dairy products (including butter). ⁴ The paleo diet includes replacing these food categories with healthy fats, including meat, fish, olive oil, eggs as well as vegetables, fruits, nuts, and seeds. Investigators have adopted a mostly ad libitum approach when researching the paleo diet in various populations.^7,8,11-14 Despite the lack of whole grains and low-fat dairy that are specified in other healthy eating recommendations, after a short-term adoption of the paleo diet, individuals with cardiometabolic diseases have been shown to reduce serum lipids. ¹⁵ The limited research available also supports an improvement of both physical risk factors and biomarkers reflecting chronic disease risk, including body weight, glycemic control, and blood pressure.^{6,8,11,13,14,16}

In addition to traditional biomarkers, leptin, brain-derived neurotrophic factor (BDNF), and fibroblast growth factor (FGF) 21 are emerging as relevant in the assessment of cardiometabolic disease risk. Leptin is a hormone produced by adipose tissue ¹⁷ that regulates energy balance and satiety, and the release and physiological response to leptin is altered with obesity. ¹⁸ Circulating levels of leptin aid in body weight regulation by signaling to the hypothalamus how much energy is stored as body fat and how much energy is consumed during meal times. ¹⁹ The effects of the paleo diet on leptin have been reported as beneficial in individuals with cardiometabolic disease,^7,14 but it is yet to be examined in overweight but otherwise healthy individuals at risk for developing cardiometabolic disease. The relationship between BDNF, metabolic health, and body weight is not well characterized in adult humans. Although BDNF is thought to play a role in energy homeostasis through its effects on energy expenditure and appetite suppression, ²⁰ lower circulating levels of BDNF were reported in individuals with high BMI but no cardiometabolic disease,^21,22 yet higher in people with type 2 diabetes. ²³ Furthermore, much of the information on BDNF is in rodent models, but there are some opposite effects of BDNF between rodents and nonhuman primates. ²⁴ Additional research on the relationship between BDNF, metabolic health, and body weight is needed in humans to determine the relationship between circulating BDNF and body weight maintenance. FGF-21 is produced by many tissues, including the liver, adipose tissue, and skeletal muscle,^25-27 with elevated levels related to various disease states and risk, including type 2 diabetes.^28-32 Several studies have evaluated the relationship between body adiposity and FGF-21,^26,29,33-36 yet the relationship remains unclear. The effects of the paleo diet on BDNF and FGF-21 are yet to be investigated.

This study examined the effects of an 8-week paleo dietary intervention on overweight but otherwise healthy physically inactive adults. Participants were coached on following the paleo diet but not on weight loss. A secondary aim of the study was to determine if this dietary approach could be practically applied over a moderate duration with high adherence when food was not provided. We hypothesized that the ad libitum, self-administered paleo dietary intervention would improve cardiometabolic disease risk factors.

Materials and Methods

Participants

Twenty-one individuals were assessed for eligibility, of whom 18 met all inclusion/exclusion criteria. The inclusion criteria were age 18 to 55 years and a body mass index (BMI) >25 kg/m². Exclusion criteria included known diagnosis of cardiovascular, metabolic (including type 1 or type 2 diabetes mellitus) or respiratory disease, smokers or smokeless tobacco users, and/or self-reported pregnancy. Seven eligible participants decided to opt-out of the study prior to the preintervention testing period. The reasons for not wanting to participate included the appearance of the diet being too expensive (n = 2), unwillingness to refrain from eating dairy and/or grains (n = 2), did not feel that the paleo diet would fit with their eating preferences (n = 2), and meal planning and food preparation seemed too complicated (n = 1). Three participants dropped out of the study part way through the dietary intervention because of not being able to keep up with the diet. Participants were recruited January to February 2014 and follow-ups occurred between January to April 2014. Eight participants consuming a typical Western diet (dairy products, cereal grains, refined sugars, refined vegetable oils, added salt), ⁴ completed the 8-week dietary intervention, and pre- and postintervention blood samples were successfully collected from 7 participants (males = 4, females = 3; Figure 1). Initial laboratory visits included a screening process during which informed consent documents were read and signed followed by the completion of a health history and physical activity questionnaire (International Physical Activity Questionnaire [IPAQ]). Data collected from the IPAQ were transformed into weekly metabolic equivalent (MET-min/wk) and only individuals categorized as low physical activity participation (<600 MET-min/wk, including intensity and duration) were eligible for participation. ³⁷ Eligible participants completed a 3-day food diary over 2 weekdays and 1 weekend day. This record was used to confirm potential participants were consuming a typical Western diet—including consumption of grains, dairy, and refined sugar. The average pre-intervention total daily energy intake (TDEI) and macronutrient distribution of the included participants was TDEI = 1853.4±441.2 kcal; 34.0% carbohydrate; 41.4% fat; 19.2% protein.

Figure 1.

CONSORT (Consolidated Standards for Reporting of Trials) diagram. Information on all participants who were enrolled in the study.

Study Procedures

In addition to the study outcome measures, this study was also utilized to determine if individuals consuming a typical Western diet could successfully adhere to an 8-week paleo dietary intervention when self-preparing food. Each participant that remained eligible following the screening process participated in preintervention testing. Blood collection and anthropometric measurements were assessed prior to and following completion of the dietary intervention period. Study protocols were reviewed by the institutional review boards at both Chatham University and the University of Houston. Written informed consent was obtained from each subject on enrollment in the study. This protocol is registered at clinicaltrials.gov NCT03814473. All subject contact was conducted at Chatham University, and sample analyses occurred at the University of Houston.

Paleo Diet Intervention Counseling and Recording

Participants were provided with a brochure providing a thorough description of the paleo diet, ~8 example recipes for each meal (ie, breakfast, lunch, dinner, and snacks; a section of recipes is included in Supplemental Figure 1 available online) included as a sample menu, and guidance to assist in shopping and self-preparation of food for the prescribed diet and to improve adherence. Participants were encouraged to consume the approved paleo diet foods—included in the brochure—ad libitum and were not coached to reduce total caloric intake (ie, they were not coached to lose weight). Additionally, weekly face-to-face meetings were held and contact information from the investigators was provided to encourage research participants to ask questions as needed between face-to-face meetings. The purpose of these meetings was to address any participant concerns regarding the paleo diet intervention, as well as to provide tactics and approaches for successful dietary modification and adherence. Participants completed 3-day food records over 2 weekdays and 1 weekend day, prior to, and during weeks 4 and 8 that were used to monitor adherence to the paleo diet (Nutritionist Pro). The 4- and 8-week food records were averaged and used as the food record for the paleo diet.

Blood Collection

Participants reported to the laboratory in a postabsorptive state (~12 hours) and rested 15 minutes in a seated position. Following the seated rest, radial pulse and blood pressure were measured and a blood sample was collected from a vein in the antecubital space. Blood was collected in serum tubes, chilled, allowed to clot, centrifuged (3000 rpm for 10 minutes at 4°C), and subsequently aliquoted into freezer tubes that were stored at −80°C until analysis. The same procedure was followed for both pre- and postintervention blood collection.

Serum Biomarkers (Primary Variables)

Resting serum cytokines—interleukin-4 (IL-4), IL-10, interferon (IFN)-γ, tumor necrosis factor (TNF)—and metabolic biomarkers—C-peptide, ghrelin, gastric inhibitory polypeptide (GIP), glucagon-like peptide (GLP) 1, glucagon, insulin, leptin, total plasminogen activator inhibitor (PAI) 1, resistan, and visfatin—were measured using magnetic bead-based assays (Bio-Plex Pro Human Diabetes Immunoassay, Bio-Rad, Hercules, CA, USA). Resting serum BDNF and FGF-21 were quantified using enzyme-linked immunosorbent assays (RayBiotech Human ELISA Kit, RayBiotech, Norcross, GA, USA). All samples were run in duplicate.

Anthropometric Measures (Secondary Variables)

Height was measured using a wall-mounted stadiometer and body weight was assessed via a calibrated digital scale.

Statistical Analyses

As our aims were partially related to feasibility, sample size was time-dependent and determined by the number of potential participants that could be recruited in a 2-month period (January 2014 to February 2014). Outcomes included anthropometric measures, resting measures, and cytokine and biomarker concentrations. Data are presented as mean ± SEM (standard error of the mean); significance is reported with P < .05 for pre- to postintervention comparisons and P < .01 for correlations. To test the difference, first the relationship between the pre value and the difference was assessed. If significance was found for the slope or intercept, each value of the preintervention difference was assessed to evaluate which parts of the preintervention variable showed a significant difference after the paleo diet; this approach used established standard errors for comparing regression lines at fixed points in the predictor space. ³⁸ Serum FGF-21 had a wide range of preintervention values and was evaluated as function of preintervention values. Effect size interpretation was the log of the ratio of means. All calculations were done in R (version 3.4) and values are reported as mean ± SEM.

Results

Eight of 11 (73%) participants successfully completed the 8-week paleo diet intervention when self-preparing food, which led to an average reduction in TDEI of 412.6 ± 124.9 kcal. No adverse side effects were reported; only dislike of following the intervention (n = 2). Only participants that completed all measures (n = 7) were included in the data analyses. There was a time effect (P < .05) pre- to postintervention for body weight and BMI (Table 1). No changes (P > 0.05) were observed in either systolic (effect size [ES] = 0.24) or diastolic blood pressure (ES = 0.01), or waist-to-hip ratio (ES = 0.01). Participants successfully changed their macronutrient distribution, such that total carbohydrates decreased by 44% (Table 2).

Table 1.

Descriptive Data Pre- and Post–Paleo Dietary Intervention.^a

	Pre	Post	P	95% Confidence Interval
				Lower	Upper
Age (years)	32.4 ± 4.9	—	—	—	—
Body mass (kg)	87.5 ± 14.0	82.2 ± 12.7*	.008	1.96	8.37
Body mass index (kg/m2)	29.4 ± 2.4	27.7 ± 2.2*	.002	0.929	2.5
Systolic blood pressure (mm Hg)	121.1 ± 4.0	118.0 ± 1.6	.292	−3.51	9.8
Diastolic blood pressure (mm Hg)	74.3 ± 2.4	73.4 ± 2.8	.695	−4.25	5.96

Values are mean ± standard error of group means.

^*Significant time effect (P < .05).

Table 2.

Dietary Data. ^a

	Pre	Paleo	P	95% Confidence Interval
				Lower	Upper
Energy (kcal)	1853.4 ± 167	1440.8 ± 111*	.016	−718	−107
Carbohydrate (g)	157.7 ± 19	88.6 ± 11*	.003	−105	−33.8
Fat (g)	85.3 ± 9	81.6 ± 9	.691	−25.7	18.2
Protein (g)	88.8 ± 9	90.2 ± 6	.885	−21.7	24.5
Total sugar (g)	54.4 ± 6	42.3 ± 7	.052	−24.2	0.138
Total fiber (g)	17.7 ± 1	17.4 ± 2	.898	−7.19	6.45

^aValues are mean ± standard error of group means. Paleo data are the average of 3-day dietary records collected during weeks 4 and 8 during the paleo dietary intervention.

^*Significant difference between pre and paleo (P < .05).

A time effect for reduced serum leptin (2796.7 ± 711.7 to 1262.9 ± 414.9 mg/dL, P = .0118, −56.2%, ES = 0.943; Figure 2) and reduced serum BDNF (1286.7 ± 135.1 to 900.8 ± 72.7 ng/mL, P = .0372, ES = 0.346; Figure 3) was observed. A reduction in serum FGF-21 as function of preintervention values was observed (160.7 ± 51.0 to 58.0 ± 17.6 pg/mL, P = .0016, ES = 1.05; Figure 4). Furthermore, the reduction in FGF-21 remained significant when changes in body mass (P = .0032) or BMI (P = .0056) were evaluated as potential predictive covariates.

Figure 2.

Serum leptin pre- and postintervention. *Postintervention leptin was lower (P < .05) than preintervention leptin.

Figure 3.

Serum brain-derived nuerotrophic factor (BDNF) pre- and postintervention. *Postintervention BDNF was lower (P < .05) than preintervention BDNF.

Figure 4.

Serum fibroblast growth factor (FGF) 21 pre- and postintervention. *Postintervention FGF-21 was lower (P < .05) than preintervention FGF-21.

No changes (P > .05) were observed for resting serum GLP-1 (ES = −0.0295), resistin (ES = −0.0936), IL-4 (ES = −0.039), IL-10 (ES = −0.202), IFN-γ (ES = −0.132), or TNF (ES = 0.12) pre- to postintervention (Table 3). One participant’s serum concentration for IL-10 was below the sensitivity of the assay (included n = 6), and 2 participants’ serum concentrations for IFN-γ (included n = 5) were also undetected.

Table 3.

Cardiometabolic Disease Biomarker Data Pre- and Post–Paleo Dietary Intervention. ^a

	Pre	Post	P	95% Confidence Interval
				Lower	Upper
Interleukin-4 (IL-4; pg/mL)	1.08 ± 0.3	1.08 ± 0.2	.986	−0.184	0.187
Interleukin-10 (IL-10; pg/mL)	6.45 ± 1.37	8.31 ± 1.70	.280	−1.45	−4.53
Interferon-γ (IFN-γ; pg/mL)	1.94 ± 0.74	2.62 ± 1.2	.402	−1.37	0.679
Tumor necrosis factor (TNF; pg/mL)	1.75 ± 0.6	1.62 ± 0.6	.581	−0.401	0.653
Insulin (mg/dL)	93.09 ± 9.05	94.30 ± 7.51	.779	−11.3	8.91
Gastric inhibitory peptide (GIP; mg/dL)	61.2 ± 5.6	60.0 ± 4.8	.749	−7.92	10.4
Glucagon (mg/dL)	104.87 ± 4.28	108.64 ± 3.82	.124	−8.94	1.39
Visfatin (mg/dL)	871.0 ± 83.1	885.21 ± 72.1	.776	−131	103
Ghrelin (mg/dL)	382.9 ± 63.1	439.4 ± 71.6	.117	−132	19
Glucagon-like peptide (GLP) 1 (mg/dL)	114.5 ± 4.9	117.7 ± 4.4	.093	−7.25	0.739
Plasminogen activator inhibitor (PAI) 1 (mg/dL)	16507.6 ± 2054.1	16585.2 ± 1078.6	.945	−2710	2550
Resistin (mg/dL)	856.1 ± 81.0	930.5 ± 72.3	.106	−170	21.2
C-peptide (mg/dL)	189.9 ± 19.0	176.5 ± 15.5	.348	−18.8	45.7

^aValues are mean ± standard error of group means.

^*Significant time effect (P < .05).

Pre-intervention, diastolic blood pressure was correlated with leptin (R² = −0.82, P = .0048); IL-4 with IL-10 (R² = 0.80, P = .0067) and TNF (R² = 0.95 P < .001); TNF with IFN-γ (R2 = 0.906, P < .001). Postintervention, IL-4 was correlated with TNF (R² = 0.93, P < .001).

Discussion

This study featured inactive overweight or obese but otherwise healthy participants who followed an ad libitum self-prepared paleo diet for 8 weeks. The primary finding of this study was that 8 weeks of an ad libitum self-prepared paleo diet reduced leptin by 56.2% in overweight and obese participants. This peptide hormone is secreted by the adipose tissue to maintain homeostatic weight and/or energy balance through satiation. ³⁹ Leptin is elevated during feeding and promotes feelings of satiation and is reduced when body fat is lost as a result of energy restriction. This results in increased energy consumption in an effort to maintain body weight and body fat homeostasis.^39,40 Obese individuals are at a greater risk of leptin resistance due to chronic elevation of circulating leptin and reduced receptor availability resulting in decreased satiation and energy expenditure. ³⁹ . As such, leptin resistance may be a contributor to obesity. ⁴¹ The paleo diet intervention in the present study resulted in large reductions in serum leptin, similar to previous reports in individuals with cardiovascular disease or type 2 diabetes.^7,14 The concomitant reduction in TDEI and body mass from the paleo diet suggests a possible improvement in leptin sensitivity. Compared with the habitual Western diet consumed by the participants prior to the intervention, the paleo diet in this study could be considered a reduced carbohydrate diet (Western: 34% TDEI vs Paleo: 25% TDEI) and more specifically, a reduced total sugar diet (Western: 54.4 g vs Paleo: 42.4 g). The participants in this study reduced their carbohydrate consumption to a level that is consistent with low-carbohydrate diets, and lower carbohydrate diets have been associated with greater satiation and lower leptin levels when compared with higher carbohydrate diets. ⁴² Furthermore, it is possible that the exclusion of cereals and grains might restore meal initiation and termination via hunger and satiety signaling by removing highly palatable food items that may interfere with the interpretation of these signals. ⁴³ The reduction in leptin is important, as other researchers have reported that leptin can be considered an independent risk factor for cardiovascular events.^44,45 Reductions of this magnitude in as little as 8 weeks suggests that the paleo diet may confer cardiometabolic benefits even when the person is not instructed to increase their structured physical exercise.

Serum BDNF was 25.8% lower after the dietary intervention. There is evidence that greater levels of circulating BDNF are associated with greater body mass and worse metabolic health in adults. Circulating BDNF in middle-aged and older adults is positively correlated with risk factors for cardiometabolic disease, including diastolic blood pressure, BMI, and fat mass in females, and diastolic blood pressure and triglycerides in males. ⁴⁶ Furthermore, serum BDNF is reported to be elevated and associated with obesity in females newly diagnosed with type 2 diabetes. ⁴⁷

BDNF may be important for body weight maintenance because it has been identified as a regulator of both food and energy as its receptor tropomyosin-related kinase B (TrkB) is found in multiple brain regions associated with food intake and metabolism. ⁴⁸ Therefore, it was surprising that the participants in this study decreased both body weight and BDNF. However, Perreault et al ²⁴ have reported that there are differences in TrkB activation when comparing rodents and nonhuman primates; indicating that extrapolating BDNF data from rodents to humans needs to be done with caution. Therefore, the relationships between circulating BDNF, body mass, and metabolic health in humans needs to be further explored.

Platelets in peripheral circulation can bind to and release BDNF when stimulated and may contribute to the difference in serum and plasma levels of BDNF. ⁴⁹ Although Lommatzsch et al ⁵⁰ found some relationship between serum and platelet BDNF, subanalyses found platelet, but not plasma, BDNF levels remained stable across multiple ages (20-60 years) and body masses (<70 kg, 70-90 kg, and >90 kg). ⁵⁰ Increased circulating BDNF, therefore, has been related to several cardiometabolic risk factors and obesity in adults. As such, a reduction in BDNF following a short-term paleo diet could potentially be considered a health benefit and reduction in disease risk.

Similar to previously reported research of diet-induced weight loss, serum FGF-21 was lower after the paleo diet.^51,52 Interestingly, the magnitude of change at the individual level was a function of their preintervention values—that is, those participants with the highest FGF-21 at preintervention had the greatest reduction. FGF-21 has been related to glucose and lipid metabolism ⁵³ and has recently been shown to be associated with weight status in humans.^{30,33,34,36,52} The literature has not supported a consistent relationship between FGF-21 and BMI in children or adults.^30,33,36,52 Some factors that may contribute to these inconsistencies include (a) sampling time, (b) assay, and (c) participant population. Lee et al, ³⁶ for example, did not observe a difference in resting serum FGF-21 in nonobese and obese participants, or a circadian rhythm that others have described ⁵⁴ despite similar participant populations and sampling intervals analyzed by different assays. FGF-21, however, has been repeatedly associated with circulating free fatty acid levels.^34,36,54 This relationship is proposed to be responsible for a sexual dimorphism observed in Danish adolescents. ³⁴ Furthermore, in body fat mass–matched obese participants, serum FGF-21 concentration was more than 2-fold higher in individuals with poor insulin sensitivity. ²⁸ It is possible, therefore, that the metabolic maladies that come with the accumulation of adipose tissue may be driving the relationship between FGF-21 and BMI. In support of this notion, obese adults with type 2 diabetes underwent a commercially available weight loss diet and experienced similar weight loss compared with the present study in 3 weeks. ⁵¹ Fasting lipids, glucose, and FGF-21 decreased relative to preintervention; however, weight loss persisted until the end of the diet (12 weeks) and FGF-21 did not decrease further. ⁵¹ Elevated FGF-21, however, has been related to coronary artery disease, nonalcoholic fatty liver disease and repeat myocardial infarction, and cardiac death.^31,32 While the relationship with weight status and BMI remains unclear, FGF-21 seems to be positively related to cardiometabolic disease risk factors and severity. As such, a reduction in FGF-21 following a short-term paleo diet is considered a health benefit and reduction in disease risk.

Although the participants were not coached to lose weight, there was a reduction in body weight and BMI (−1.5 kg/m²). This change may be attributed to a limitation in “allowed” foods. Despite the decrease in BMI, there was but no changes in blood pressure. However, the reduction in BMI does confer health benefits on its own.^1,55 The participants in the present study did not have high blood pressure, and this may be why there was not a change in blood pressure. Other researchers have reported significant changes in systolic and diastolic blood pressure after a short-term paleo dietary intervention.^11,13,16 In the studies from other groups, both Österdahlet al ¹¹ and Frassettoet al ¹⁶ used similarly aged healthy inactive participants and report a significant decrease in diastolic blood pressure. The participants in the aforementioned studies, however, had a lower average preintervention BMI than our participants and this may account for the lack of response in the present study.

Although not instructed to consume fewer total calories, there was a reduction in overall TDEI and dietary carbohydrate. The change in TDEI and dietary macronutrient composition were expected, as one of the major tenants of the paleo diet is the exclusion/avoidance of cereals and grains. Furthermore, on a per-calorie basis the paleo diet has previously been reported as more satiating than the Mediterranean diet. ⁷ While we did not measure satiety directly, the resultant TDEI deficit during the ad libitum paleo diet compared with the preintervention Western diet supports this concept. Long-term energy balance influences weight loss, gain, or maintenance. Commonly, weight loss interventions are conducted using both intentional caloric restriction and increased physical activity. As such, this appears to be a positive effect of the paleo diet for the free-living dieter seeking weight-related health benefits^1,55 that may not want to consciously restrict their diet.

There are some limitations to this research study. It is widely accepted that participants underreport dietary intake on food diaries, and we relied on the participants to accurately report their specific food items. However, unless the participants are under 24-hour monitoring in a controlled research environment—which is not very applicable to “real-world” settings—dietary monitoring in research studies is a limitation. This study only examined people who perform low amounts of physical activity. This was by design, as the focus of this study was the paleo eating pattern independent of exercise training performance. There was also a small sample size and high rate of people who were screened for participation/enrolled in the study but did not start or complete the study. This was our first study with the paleo eating plan, and as such an aim was to determine the feasibility of our design. In addition, the ES for the many of variables support the strength of our findings.

The results of our study are not in complete agreement with previously published results on the paleo diet, but the design of these studies vary by factors including length of diet and study population.^6,11-13,16 Additionally, unlike other studies we did not have a comparison group,^7,8,13 because our intent was to make conclusions against the participant’s preintervention values and to determine if our participants could follow a paleo diet ad libitum and when self-administered. Taken together, our study demonstrated that an ad libitum, self-prepared paleo diet can be followed for at least 8 weeks and result in the reduction of multiple cardiometabolic disease risk factors in free-living dietary research participants provided with dietary substitution suggestions rather than food.

In conclusion, 8 weeks of following the paleo diet resulted in improvements in body weight and novel biomarkers linked to cardiovascular disease and type 2 diabetes. These improvements result when the participants were only coached to change dietary eating plan—not to reduce body weight. Longer term interventions are required to determine the continued effect of the paleo diet and if the reduction in body weight is maintained. This study demonstrates, however, that research participants can shop for and prepare their own food to follow a paleo diet intervention and reduce body weight without specific coaching on weight loss. Furthermore, given the current popularity of the paleo diet the potential improvements in cardiometabolic disease risk factors is an encouraging finding.