What’s a Paleo Diet?
The premise of the paleo diet is that genetically we haven’t changed much since the time of the earliest humans. It has been said that “From a genetic standpoint, humans living today are Stone Age hunter-gatherers displaced through time to a world that differs from that for which our genetic constitution was selected” (Eaton, Konner, & Shostak, 1988).
Hunter-gatherer populations such as the Inuit, Australian Aboriginals, Hadza and others have until recent times lived relatively healthily and with a significant absence of the metabolic disorders of obesity and diabetes that plague the modern, western world. (O'Dea, 1991a, 1991b; O'Keefe, Cordain, Harris, Moe, & Vogel, 2004; Sinclair, 1953).
The ‘modern’ Paleo diet seeks to emulate these traditional hunter-gatherer diets by eliminating foods that are abundant in the modern diet but that were not present (in large amounts) in the diets of most hunter-gatherers. There are a many variations on the Paleo theme but in general the following constitutes the Paleo guidelines:
- Free range, organic meat, eggs, fish
- Nuts and seeds
- Fibrous vegetables
- Root vegetables (sweet potato, yams etc.)
- Berries and fruit
- Virgin nut and fruit oils (olive, macadamia, coconut)
- Factory farmed meats
- Battery eggs
- Grains and legumes
- Seed oils
Critics of the Paleo diet point to the lack of consistency in hunter-gatherer diets. In other words there is no ‘one true’ hunter-gatherer diet. For example analysis of 229 hunter-gatherer diets from around the world found a high variance in carbohydrate intake (approximately 3%-50% of daily calories). However the authors noted that carbohydrate intake in almost all hunter-gatherer populations is lower than that currently recommended for health(Ströhle & Hahn), and it’s fair to say that all hunter gatherer populations have an absence of refined and processed foods!
What does the Science say?
At present there’s a limited amount of research on the Paleo diet, and it’s a hard diet to study as it has no defined macronutrient (protein, carb and fat) percentages or recommendations. There have been a few studies though, most of which included women and show positive outcomes for weight loss, satiety (feelings of satisfaction and fullness) and blood markers that are indicators of both metabolic and cardiovascular health.
- Paleo diets may reduce cholesterol, LDL cholesterol, triglycerides, insulin and blood pressure (Frassetto, Schloetter, Mietus-Synder, Morris, & Sebastian, 2009; Masharani et al., 2015)
- A Paleo meal may provide greater satiety than a standard meal based on ‘best-practice’ dietary guidelines(Bligh et al., 2015) or a best-practice diabetic meal plan (Jönsson, Granfeldt, Lindeberg, & Hallberg, 2013)
- The Paleo diet appears to be more satiating than the Mediterranean diet (Jonsson, Granfeldt, Erlanson-Albertsson, Ahren, & Lindeberg, 2010)
- A randomised controlled trial featuring nine men and 25 women found that a Paleo diet resulted in lower blood pressure, cholesterol, triglycerides and higher HDL cholesterol than the reference diet over two weeks. No differences were noted for intestinal permeability (‘leaky gut’), inflammation or salivary cortisol
- In a two year randomised controlled trial post-menopausal women lost more fat at six months and had lower triglycerides at six and 24 months (Mellberg et al., 2014)
- Ten healthy post-menopausal women ate an ad libitum (eat as much as you want) Paleo diet for 5 weeks. Average calorie intake was reduced by 25% and average weight loss was 4.5kg along with reduced waist and hip circumference, blood pressure, fasting glucose, cholesterol, triglycerides and LDL cholesterol (fat in the liver – a marker for metabolic disorder was also decreased.) (Ryberg et al., 2013)
- A randomised cross-over trial featuring ten men and three women demonstrated that Paleo diets have a lower glycaemic index and is lower in total energy compared to a diabetic diet. The Paleo diet resulted in lower HbA1c (a measure of average blood sugar levels), triglycerides, blood pressure and higher HDL cholesterol.
- One uncontrolled trial of 24 males and 20 females followed a Paleo diet for ten weeks. Interestingly those with good cholesterol profiles appeared to worsen (reduced HDL and increased LDL) with no change in those with sub-optimal blood lipids at baseline. This suggests that there could be a worsening of blood profiles with some Paleo diets (it’s important to interpret these results with care as they didn’t evaluate lipid sub-fractions) (Smith, Trexler, Sommer, Starkoff, & Devor, 2014)
Is Paleo OK for Women?
The few trials that have been performed on the Paleo diet and those including women specifically appear to overwhelmingly show benefits with no adverse effects reported.
Much of the criticism of Paleo diets for women come from the assumption that a Paleo diet is low in carbohydrate and that this might negatively affect thyroid status or cause other hormone imbalances. However the Paleo diet isn’t by nature low in carbohydrates as it can (depending on how it’s applied) include appreciable carbohydrate from sweet potato, yams, vegetables, berries and some fruit, which would be more than adequate for most women.
Paleo and Hormones
There is no good reason to think that a Paleo diet would negatively affect hormone levels. However a severely carb restricted Paleo diet might affect hormone levels in some women. Carbohydrate restriction can increase cortisol levels (one of our major stress hormones) and reduce levels of the sex hormones (especially tesosterone). This cortisol to free testosterone ratio is a key marker of fatigue syndromes. It is important to note that much of these distortions may occur in the transition phase to a lower carbohydrate diet, but may not last if one becomes sufficiently ‘fat adapted’.
Some women do find that going extremely low with carb intake does distort hormone levels, leading to resistance to weight-loss, poor mood and cognition, and altered menstrual cycles. This can typically be rectified with the addition of small amounts of natural, unprocessed carbs back into the diet. Stephanie Greunke RD (on Rob Wolff’s blog) has this to say with regard to to her own hormonal problems on a very low carb diet and how she dealt with them: “We didn’t have to start throwing back pounds of sweet potatoes and rice, we just needed to quit the chronic very low carb (<50ish grams) lifestyles that we were on and add in some root veggies and fruit” (Greunke, 2015)
Paleo and thyroid function
Diets that have reduced carbohydrate (typically under 35% of calories) can reduce levels of the active thyroid hormone triiodothyronine (T3) (Phinney, Bistrian, Wolfe, & Blackburn, 1983) without affecting thyroxine (T4) or thyroid stimulating hormone (TSH) levels (Fery, Bourdoux, Christophe, & Balasse, 1982; Ullrich, Peters, & Albrink, 1985; Yancy Jr, Foy, Chalecki, Vernon, & Westman, 2005; Yancy, Olsen, Guyton, Bakst, & Westman, 2004). Stephen Phinney and Jeff Volek, two of the foremost low-carb researchers have noted that there is no difference observed in T3 uptake between a very low carbohydrate diet group and a control diet and that metabolic rate isn’t affected and that people on low carb diets don’t express symptoms of hypothyroidism. It seems likely then that that reducing carb intake may reduce T3 levels without necessarily affecting someones health (Phinney et al., 1983; Volek et al., 2002).
Paleo provides a framework or ‘concept’ for healthy eating that is easily understood. It is not necessarily restrictive in any nutrient and so should provide no real detriment to health. It’s not for everyone though, and not everyone needs to avoid all grains, legumes or dairy. Likewise people need to find their own level of carb tolerance and this is especially true for women as a severely restrictive low-carb version of the Paleo diet may be problematic.
Carb intake is highly individual and depends on a) how active you are, b) how ‘tolerant’ you are to carbohydrates and c) what type of exercise you are perfoming.
You may need (just a little!) more carbohydrate from natural, whole, unprocessed sources if:
• If you are extremely active
• If you perform high intensity exercise such as CrossFit or intensive circuit training
• If you are having trouble recovering from workouts
• If you have an underactive thyroid
• If you are chronically fatigued
• If you lose your period or are having irregular cycles
• During pregnancy and breastfeeding
Listen to your body and if what you’re doing doesn’t make you feel great then something has to change. It could be that you need to avoid a particular food…or add one back in…or eat a little more carbohydrate…or a little less! We are all uniquely individual and there is no one-size-fits-all diet prescription.
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