Keto vs. Plant-Based Diet Put to the Test — Which Won?
In a recent study financed by the NIH, health people were put into a randomized controlled trial to test out two competing models of obesity: the carbohydrate-insulin model supported by the keto diet and the passive overconsumption model concept of the plant-based diet.
This was the most controlled study ever done putting these two theories to test. Which one lived up to their claims? Let real science tell us the answer.
The Carbohydrate-Insulin Model
According to the Carbohydrate-Insulin Model (CIM) of obesity, high-glycemic carbohydrates results in high postprandial insulin spikes, which results in hormonal responses that lead to the promotion of fat storage while increasing hunger and energy intake, or lower energy expenditure.
As the theory follows, starchy and sugary meals with high glycemic load result in increased insulin levels in the blood, which lower the circulation of all major metabolic fuels from the body that stimulates energy expenditure by increasing glucose uptakes into tissues, suppressing the release of fatty acids from adipose tissue, inhibiting the production of ketone bodies in the liver, and while promoting fat and glycogen deposition.
The idea behind ketosis and weight loss is that ketone bodies produced by the liver during periods of fasting, starvation, chronic and excessive alcohol intake, prolonged intense exercise, and in low-carb diets, replace glucose as the main, and more efficient, fuel for the body
The theory proposes that these metabolic responses from the consumption of high glycemic carbohydrates promote the deposition of calories in fat cells instead of oxidation of calories in lean tissues, leading to weight gain via increased hunger and a slower metabolic rate, which leads to a number of chronic conditions like diabetes.
Also, they claim that low-fat/high-carb diets further restrict energy availability in the blood, triggering starvation responses characterized by increased hunger, poor metabolic rate, and elevated stress hormone levels.
The Passive Overconsumption Model
Alternatively, proponents of low-fat/high-carb diets propose that high fat intake promotes the storage of body fat over time due to passive overconsumption of energy based on the higher energy density nature of fat cells.
Despite higher postprandial glycemic spikes in comparison to a low-carb diet, advocates of a low-fat/high-carb diet argue that what promotes fat storage in the body is fatty blood resulting from fatty meals, especially from animal products, which are rich in saturated fat and cholesterol. The accumulation of lipids in the bloodstream leads to fatty cells that promote insulin resistance and glucose intolerance, which characterizes type II diabetes.
Proponents argue that carbohydrates are the main preferable fuel of the body and that the types of carbohydrates matter. A whole-food, plant-based, diet is rich in fiber which regulates our appetite while optimizing our energy intake at lower rates of body fat, especially insoluble fiber which contains virtually zero calories.
They claim that a high-fat/low-carb diet puts our body into extreme stress, leading to the accumulation of body fat, especially in the arteries, despite the production of ketone bodies, which triggers the development of metabolic disorders that culminate into undesirable chronic diseases in the long-run, including diabetes and cardiovascular diseases.
The Study — Settings
In a hospital setting, 20 non-diabetic adults (11 male and 9 female) with a mean age of 29.9 years and a mean BMI of 27.8 were admitted as inpatients to the NIH Clinical Center where tests were conducted for a continuous 28-day period.
Subjects were randomly assigned to either an animal-based, ketogenic, low-carb diet (ABLC) or a plant-based, low-fat diet (PBLF) for 2 weeks and then immediately switching to the alternative diet for a subsequent 2-week period. Both diets were whole-food based.
In order to avoid biased eating patterns, subjects were told that this wasn’t a weight-loss study and asked to follow an ad libitum protocol, meaning that there would be no caloric restriction. They were given 3 daily meals at standardized times and a continuous supply of snacks and water. Meals were time-restricted (60 min each) and daily calories were provided at twice each subject’s estimated energy requirements (1.6 x resting energy expenditure or BMR).
Protein levels were adjusted for this test. The ABLC diet was composed of 14.2% protein/75.8% fat/10% carbohydrate and had an energy density (beverage excluded) of 2.2kcal/g. On the other hand, the PBLF diet had a macro of 14.5% protein/10.3% fat/75.2% carbohydrates and a non-beverage energy density of 1.1 kcal/g.
Exercising wasn’t part of the protocol and physical activity expenditure was measured as the difference between 24-hour energy expenditure and sedentary energy expenditure.
A battery of tests, including daily weight, ketone bodies, body fat scans, inflammation markers, and continuous glucose measurements in both fasted and postprandial settings, among others, were applied daily to blinded subjects.
The Test Results
Food Intake
Over the 2-week testing period, the PBLF was 689±73 kcal/day lower than the ABLC diet. During the second week of each diet period, energy intake was 544±68 kcal/day lower during the PBLF diet phase, showing consistent results.
All participants consumed less energy during the PBLF diet compared to the ABLC diet over the course of the 24 weeks. The energy density of the PBLF diet was significantly lower (0.96±0.03 kcal/g) than that of the ABLC diet (1.9±0.03 kcal/g). At the same time, the total mass of food was greater in the PBLF group (2140±43 g/day) than the ABLC group (1473±43 g/day). In other words, the PBLF group ate more in volume and less in calories.
Appetitive Measurements & Eating Rate
There were no significant differences in the reported pleasantness or familiarity between the PBLF and ABLC groups on a continuous 100-point visual analogue scale. Also, there were no significant differences in hunger, satisfaction, fullness, or eating capacity despite large differences in energy intake.
The higher energy density of the ABLC meals (44.2±0.99 kcal/min) resulted in a faster energy intake rate compared with the PBLF meals (30.9±0.99 kcal/min).
Bodyweight & Composition
Bodyweight decreased in both diets, but total weight loss after 2 weeks was slightly greater (1.77±0.32 kg) with the ABLC diet in comparison to the PBLF diet (1.09±0.32 kg). Initial weight loss in the first week of each diet was also greater in the ABLC diet.
However, analysis of fat-free mass change measure by dual-energy X-ray absorptiometry revealed that most of the weight changes with the ABLC diet (-1.61±0.27 kg) were due to changes in fat-free mass as the figure below shows. On the other hand, the PBLF diet (-0.16±0.27 kg) did not result in a significant change in fat-free mass.
At the same time, the ABLC diet didn’t result in a significant change in body fat during the first week (0.09±0.12 kg) and second week (-0.18±0.19 kg), whereas the PBLF diet resulted in significant changes in fat mass after the first week (0.27±0.12 kg) and the second week (-0.67±0.19 kg).
Even though there were no statistically significant differences in the final amount of body fat lost at the end of both diet periods (0.48±0.27 kg), the differences in the average rate of body fat loss between the diets was 35±14 g/day, with the PBLF diet resulting in body fat loss at an average rate of 51±9 g/day vs. 16±9.7 g/day with the ABLC diet.
Continuous Glucose Monitoring & Glucose Tolerance
The PBLF diet resulted in greater mean postprandial glucose levels (94.3±1.6 mg/dl) and its coefficient of variation (18.4±0.5 %) in comparison to the ABLC diet (81.3±0.6 mg/dl) and respective CV (13.5±0.5 %).
An oral glucose tolerance test (OGTT) revealed that the ABLC diet resulted in a relative impairment of glucose tolerance compared to the PBLF diet. Mean glucose was 115.6±2.9 mg/dl with the PBLF diet and 143.3±2.9 mg/dl with the ABLC diet.
Postprandial glucose levels measured 2 hours after was 108.5±4.3 mg/dl with the PBLF diet and 142.6±4.3 mg/dl with the ABLC diet. Glucose levels ≥140 mg/dl threshold after 2 hours — a marker of impaired glucose tolerance — was found in 9 subjects during the ABLC diet as compared to a third (3) of these same subjects during the PBLF diet.
No significant differences in mean insulin were found, though the PBLF group was slightly lower (85.5±6.6 µU/ml) in comparison to the ABLC group (97.8±6.6 µU/ml).
On the other hand, mean free-fatty acids were significantly lower in the PBLF diet (174.8±21 µmol/L) in comparison to the ABLC diet (346.5±21 µmol/L)
Blood Pressure & Pulse Rate
The PBLF diet resulted in significantly lower systolic blood pressure (112.2±0.4 mmHg), diastolic blood pressure (66.9±0.4 mmHg), and pulse rate (72.6±0.5 bpm) in comparison to the ABLC diet (SBP 115.8±0.4 mmHg; DBP 68.5±0.4 mmHg; PR 76.9±0.5 bpm)
Fasting Blood Measurements (Summary)
- Glucose and insulin significantly decreased compared to baseline with both ABLC and PBLF diets but were not significantly different from each other.
- Free fatty acids increased from baseline with both diets, but to a significantly greater degree with the ABLC diet. On the other hand, triglycerides increased from baseline with the PBLF diet and decreased with the ABLC diet.
- Total and LDL cholesterol decreased significantly on the PBLF diet as compared to both baseline and the ABLC diet which were not significantly different from each other.
- VLDL particle numbers decreased from baseline with the ABLC diet and increased with the PBLF diet, but there were no significant differences in VLDL particle size.
- LDL particle number decreased with the PBLF diet and increased with the ABLC diet. The ABLC diet led to a shift in LDL particle size distribution towards a greater number of small LDL particles.
- Both HDL cholesterol and apolipoprotein-A-1 decreased from baseline with both diets, but to a greater extent with the PBLF diet. Apolipoprotein-B concentrations significantly decreased from baseline with the PBLF diet but slightly increased with the ABLC diet.
- Inflammatory markers C-reactive protein (hsCRP) and GlycA were both significantly decreased from baseline with the PBLF diet whereas only GlycA was reduced with the ABLC diet, but to a significantly greater extent than the PBLF diet.
Other important markers were included, including C-peptides, ketone bodies, branched-chain amino acids, thyroid hormones, uric acid, and others. The complete list can be checked on the study (reference page).
Discussion
As expected, the PBLF diet had a much higher glycemic load and resulted in greater postprandial glucose and insulin levels compared to the ABLC diet. However, the ABLC diet showed higher glucose sensitivity and insulin resistance, suggesting a pattern of pre-diabetes.
The CGM measurements of interstitial glucose concentrations showed that both mean and postprandial glucose levels were much larger in the PBLF diet as compared to the ABLC diet. This is of potential concern because high glucose variability is thought to be a risk factor for coronary artery disease, though changes in plasma glucose tend to precede changes in interstitial glucose, thus, providing an earlier signal concerning hypo- and hyperglycemia.
Despite the significantly higher energy intake in the ABLC diets, total weight loss after 2 weeks was similar. However, most of the weight loss in the ABLC diet was mainly from water and fat-free (lean) mass, whereas the PCLF diet promoted a significant loss of body fat, which the ABLC did not. Thus, contrary to the carbohydrate-insulin model theory, more body fat was lost with the PBLF diet as compared to the ABLC Diet.
The ABLC diet resulted in decreased fasting triglycerides compared to baseline whereas the PBLF diet increased fasting triglycerides, though there was no distinction between saturated and unsaturated fatty acids. However, postprandial triglycerides were higher in the ABLC following a low-carb test meal compared to the isocaloric low-fat test meal. Both fasting and postprandial triglycerides are thought to increase the risk of CVD though not a direct atherogenic factor according to this review from the AHA.
On the other hand, the PBLF diet showed better levels of fatty acids in comparison to the ABLC diet. Free-fatty acids are independently associated with cardiovascular mortality, representing a better marker for cardiovascular disease prevention.
Surprisingly, the ABLC diet tended to shift the LDL particle size distribution towards smaller particles as compared to baseline which is the opposite of what is expected for low-carbohydrate diets. Smaller LDL particles are more atherogenic in nature than larger LDL subfractions, potentializing the risk for CHD or atherosclerosis and CVD.
Both diets led to decreases in HDL (good) cholesterol and APOA-1 compared to baseline, but these parameters were decreased to a greater degree with the PBLF diet. At the same time, the PBLF diet resulted in decreased total cholesterol, LDL cholesterol, and apolipoprotein-B concentrations, which didn’t happen with the ABLC diet.
Despite the similar protein content of the ABLC and PBLF diets, protein intake during the ABLC diet was increased as compared to the PBLF diet. However, the higher protein intake in the ABLC diet didn’t increase satiety and decrease energy intake as expected. The PBLF diet led to a significantly lower non-beverage energy density, likely due to the much higher dietary fiber intake.
The Bottom Line
The carbohydrate-insulin model of obesity failed to live up to its claims. Despite having higher postprandial insulin levels, the PBLF group lost significantly more body fat in comparison to the ABLC group throughout both test phases, while differences in hunger parameters weren’t significant, hence, challenging the validity of the model.
On the other hand, the PBLF group ate more carbohydrates but had lower energy density meals in comparison to the ABLC group; however, the higher energy density meals of the ABLC group didn’t lead to net body fat gain, challenging the validity of the passive overconsumption model (though test duration was probably a significant factor for this).
Despite being a short-term study, this is the best RCT testing the theories behind the keto vs. the plant-based diet concerning ad libitum energy intake and subsequent fat gain. It’s clear that the relationship between energy intake and body fat accumulation is much more complex than what those two models propose.
In summary, the whole-food, plant-based diet led to more volume of lower-density meals and more body fat loss. In contrast, the whole-food keto diet led to less volume, higher-density, meals and lost more total weight from water and lean mass.
It’s not about which diet is better, but which is healthier based on scientific evidence — and the plant-based diet is always the winner. Nothing more to declare, your highness!
Peace & stay plant-based!🌱✌
Study Reference
Hall, Kevin D., et al. “A Plant-based, Low-fat Diet Decreases Ad Libitum Energy Intake Compared to an Animal-based, Ketogenic Diet: An Inpatient Randomized Controlled Trial.” NutriXiv, 6 May 2020. Web.
