Opening Comments

Welcome back, everyone, for part 2 of my Paleo critique. If you are just joining me I highly suggest going back and reading last week’s article before proceeding. However, for those of you who are lazy, in the interest of time I will copy and paste my concluding remarks from last week, here, so that we’re all caught up.

“Not only do Paleo advocates follow a rigid diet based on loose assumptions of ancestral food patterns (which they’re wrong about in the first place), but they also make adjustments to their philosophy where they see fit, even if it deviates from their core principles. To me it just sounds like an excuse to impose one’s own views about nutrition on others.” 

Now that we’ve got that out of the way, I would like to pick up this week by looking at the limited research that compares the Paleo diet to some more traditional diets on various metabolic risk factors and satiety. Now, before we begin, I would like everyone to remember: the point of the Paleo diet is not the ratios of protein, carbohydrate, and fat. Paleo nuts could care less about strict dietary ratios. Rather, the Paleo diet is about the types of foods that can and cannot make up those proportions. If you have to, refer back to the list of ‘foods to consume’ and ‘foods to avoid’ in last week’s article.This is important when reviewing the literature on Paleolithic diets because there must be compelling evidence that it is the food choices of the Paleo diet that are beneficial to health and not the ratios of those foods. This is, in fact, the primary focus of today’s discussion. That being said,I will start by going in order from the earliest to the most recent study, and then I’ll try to tie things up and make some final comments about Paleo diets in general.

Lindeberg et al. 2007

In one of the first studies looking at Paleolithic diets, researchers Lindeberg et al. saw that a Paleolithic diet improved glucose tolerance more than a Mediterranean-like diet in individuals with ischemic heart disease and impaired glucose tolerance [1]. This, however, is not surprising given that the Paleo group consumed fewer calories (450kcals less) and significantly fewer carbohydrates (CHO) than the Mediterranean group.

Above, I’ve provided a screen shot of the daily intakes of CHO between the two diet-groups (Paleo is the left column, Mediterranean is the right column). As you can see, the Paleo group consumed about 97g (or 42%) fewer carbohydrates than the Mediterranean group. On the other hand, the protein content between the groups did not differ by any significant degree (90g vs. 89g), nor did the fat content (42g vs. 50g). However, the failure to account for equal macronutrition between the two groups makes it hard to determine the actual impact of the Paleo food choices rather than just having an ideal ratio of protein to CHO. In fact, a substantial amount of research done by Donald Layman, at the University of Illinois at Urbana-Champaign, shows that having a higher protein to CHO (PRO:CHO) ratio helps to improve glucose homeostasis in individuals, especially during weight loss [2-6]. What’s more, Layman’s subjects were definitely not eating a Paleolithic diet!

Frassetto et al. 2009

In the next study, Frassetto et al. saw that compared to usual dietary habits, a Paleolithic-style diet improved glucose tolerance, insulin sensitivity, blood pressure, and lipid profiles, independent of weight loss, in nine sedentary, overweight subjects [7]. Again, the results are not surprising given the poor, prior dietary habits of the participants. Below, the screenshot clearly shows that the usual intakes of subjects were higher in saturated fats, cholesterol, and sodium, while being lower in mono- and polyunsaturated fats, protein, and some other micronutrients.

Also, if you look closely, you will see that protein is almost twice as high while on the Paleo diet, therefore increasing the PRO:CHO ratio and possibly explaining the reason for the improved glucose tolerance. However, the small sample size and failing to control for macronutrition (again) makes this a weak study and still leaves us questioning whether or not excluding grains, dairy and sugars truly is optimal for human health, rather than just eating less CHO and more protein.

Jönsson et al. 2009

Jönsson et al. examined the effects of a Paleolithic diet on glycemic control and several risk factors for cardiovascular disease (CVD) over a 3-month period in patients with type 2 diabetes [8]. They found that the Paleo diet was superior to a traditional diabetic diet for improving glycemic control and CVD risk factors. Like the previous two studies, the results, again, are not surprising given the greater reduction in calories (300kcals less) and CHO (71g less) in the Paleo group compared to the control. Furthermore, the protein content of the diet was 4% higher in the Paleo group compared to the control (24% and 20%, respectively), again, altering the PRO:CHO ratio. Anyone else seeing a pattern here?

Similarities & Failures

As you can see, the failure for each study to accurately control for overall calories and macronutrient composition between diet groups – specifically protein and CHO – makes it hard to conclusively say that a hunter-gatherer style diet – i.e. one devoid of post-agricultural foods – is truly superior for human health. Stronger study protocols would have had control groups with matching macronutrition equal to that of the Paleo group’s diet. That way, any differing results seen between the two groups could be attributed to the food choices and nothing else. However, given their failures to do so, not much can be concluded from the aforementioned studies other than having more protein and less CHO seems to be beneficial in terms of certain metabolic risk factors, specifically glucose/insulin homeostasis. Still, the question remains whether or not the specific types of CHO, proteins, and fats – as strictly recommended by the Paleo diet – are superior for human health when compared to more conventional diets. Obviously, switching to a diet that automatically restricts entire food groups high in CHO is an easy way to both cut calories and reduce overall CHO intake, the point is that the source of CHO may not matter more so than the overall amount of CHO in the diet. Therefore, Paleolithic nutrition may not be driving force for the results given certain confounding factors such as the PRO:CHO ratio in the diet and the greater reduction in overall caloric intake. Until better studies are conducted, the Paleo diet and its benefits on health markers is still speculative and nothing more.

Now, there is still one study left which I have yet to talk about, however, this study deals more with satiety rather than metabolic risk factors. Either way, it still has its implications for weight loss/control and overall health and therefore should not be discarded in today’s discussion.

Jönsson et al. 2010

The last study we will look at found that a Paleolithic-style diet was more satiating per calorie than a Mediterranean diet in 29 subjects with ischemic heart disease [9]. As you might remember from my previous article on beverages and satiety, satiety simply means fullness. On average, participants in the Paleo group consumed about 435 fewer calories than the Mediterranean group. Furthermore – as shown below – the protein content of both diets was similar (92g vs. 88g) even though the percentages of protein in the diets were significantly different (27% Paleo vs. 20% Mediterranean).

You will also notice the 82g difference in CHO intake between the two groups. Taken together, this drastically increases the PRO:CHO ratio, essentially making the Paleo diet nothing more than a low-CHO diet. To quote the authors themselves;

“The Paleolithic diet in this study plays out as a low-carbohydrate diet, and the term effects on weight loss from low-carbohydrate diets suggesting greater satiety could be the controlling factor behind the greater satiating effect of the Paleolithic diet in this study.”

This is important because there is accumulating evidence that diets higher in percentages of protein are more satiating than those with lower percentages protein, in both short-term and longer-term studies [3-5, 10-16]. Furthermore, another aspect of the Paleo diet was that it was considerably higher in fruit intake compared to that of the Mediterranean group (513g/day vs. 262g/day, respectively). In a study that produced a validated satiety index of commonly consumed foods, researchers saw that fruit was the most satiating food, even edging out that of protein-rich foods, as a group [17]. Therefore, given the ad libitum nature of the study – simply meaning they ate at their leisure – as well as the differences in diet protocols, it is not surprising that the diet with the higher PRO:CHO ratio and higher in fruit was more satiating than the diet that was lower in both.

Summary

So, to wrap things up, it seems that the benefits of a Paleo diet – i.e. a diet without starches, sugars and dairy – are still left up to debate. In no way did the studies above provide any insight into whether or not Paleo recommendations are better than just having a lower-carbohydrate diet with higher percentages of protein (at least in sedentary/health compromised populations). A much stronger set of studies would have had control groups with isocaloric diets and equal levels of PRO, CHO, and fats that vary only in the types of foods that comprise those ratios. Until then, the beneficial aspects of the Paleo diet are still theoretical and not much more. Obviously, eating a diet lower in refined grains and processed products will be much healthier than one that is higher in those types of foods. However, to dogmatically restrict entire food groups which CAN and DO offer health benefits is nothing more than someone imposing their own flawed views of nutrition on others. What ever happened to moderation? My suggestions are to eat a well-rounded and balanced diet, which is diverse in the amounts and types of foods you consume, in order to maximize the benefits from each source. Dichotomous thinking about nutrition always leads to more bad than good, remember that.

References

1. Lindeberg S, Jönsson T, Granfeldt Y, Borgstrand E, Soffman J, Sjöström K, Ahrén B. A Paleolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischemic heart disease. Diabetologia 2007;50:1795-1807.

2. Layman DK, Clifton P, Gannon MC, Krauss RM, Nuttall FQ. Protein in optimal health: heart disease and type 2 diabetes. Am J Clin Nutr. 2008;87(5):1571S-1575S.

3. Layman DK. Dietary guidelines should reflect new understandings about adult protein needs. Nutr Metab. 2009;6:12.

4. Layman DK, Baum JI. Dietary protein impact on glycemic control during weight loss. J Nutr. 2004;134(4):968S-73S.

5. Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD. A reduced ratio of carbohydrate to protein improves body composition and blood lipid profiles during weight loss in adult women. J Nutr. 2003;133(2):411-7.

6. Layman DK, Shiue H, Sather C, Erickson DJ, Baum J. Increased dietary protein modifies glucose homeostasis in adult women during weight loss. J Nutr. 2003;133(2):405-10.

7. Frassetto LA, Schloetter M, Mietus-Snyder M, Morris RC, Sebastian A. Metabolic and physiologic improvements from consuming a Paleolithic, hunter-gatherer type diet. Eur J Clin Nutr. 2009;63:947-955.

8. Jönsson T, Granfeldt Y, Ahrén B, Branell UC, Pålsson G, Hansson A, Söderström M, Lindeberg S. Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: a randomized cross-over pilot study. Cadriovasc Diabetol. 2009;8:35.

9. Jönsson T, Granfeldt Y, Erlanson-Albertson C, Ahrén B, Lindeberg S. A Paleolithic diet is more satiating per calorie than a Mediterranean-like diet in individuals with ischemic heart disease. Nutr Metab. 2010;7:85.

10. Halton TL, Hu FB. The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. J Am Coll Nutr. 2004;23(5):373-85.

11. Veldhorst M, Smeets A, Soenen S, et al. Protein-induced satiety: effects and mechanisms of different proteins. Physiol Behav. 2008;94(2):300-7.

12. Westerterp-Plantenga MS. Protein intake and energy balance. Regul Pept. 2008;149(1-3):67-9.

13. Lejeune MP, Westerterp KR, Adam TC, Luscombe-Marsh ND, Westerterp-Plantenga MS. Ghrelin and glucagon-like peptide 1 concentrations, 24-hr satiety, and energy and substrate metabolism during a high-protein diet and measured in a respiration chamber. Am J Clin Nutr. 2006;83(1):89-94.

14. Smeets AJ, Soenen S, Luscombe-Marsh ND, Ueland Ø, Westerterp-Plantenga MS. Energy-expenditure, satiety, and plasma ghrelin, glucagon-like peptide 1, and peptide tyrosine-tyrosine concentrations following a single high-protein lunch. J Nutr. 2008;138(4):698-702.

15. Keller U. Dietary proteins in obesity and in diabetes. Int J Vitam Nutr Res. 2011;81(2-3):125-133.

16. Westerterp-Pantenga MS, Nieuwenhuizen A, Tomé D, Soenen S, Westertetp KR. Dietary protein, weight loss, and weight maintenance. Annu Rev Nutr. 2009;29:29-41.

17. Holt SHA, Miller JC, Petocz P, Farmakalidis E. A satiety index of common foods. Eur J Clin Nutr. 1995;49:675-690.