Legumes. There is confusion amongst people as to their place in a paleo diet, particularly people who choose to eat a vegetarian diet, this presents an immediate roadblock in their mind: what do I eat if I can’t eat beans? Historically the original ‘paleo’ diet does not recommend legumes as part of the plan – equally this paleo prescription necessitates omitting dairy, starch and cautioning against the consumption of saturated fat. Fast forward to 2014, advocates of the paleo approach to eating are inclined to use evidence to support a diet we believe is optimal for health, rather than rely on historical, emotive and scientifically questionable arguments to underpin eating for health.
The main reason we don’t make a song and dance about legumes is they aren’t worth making a song and dance over, really. They aren’t that nutrient dense when they go head to head with animal sources of protein. If you adopt a paleo diet and choose legumes over animal protein then you’re not maximising nutrient density, one of the fundamental principles of a paleo approach to diet. The more nutrient dense foods we eat, the more nutrients we absorb through our diet and the better our body functions. The original argument for avoiding them is largely around the lectins that are compounds contained in the raw bean or pea. These can cause leaky gut and inflammation and a lot of associated gastrointestinal problems. The research that underpins this argument is based on animal studies. That in itself isn’t the problem; many important dietary discoveries begin with a mice or rat model to test a hypothesis. In the mice studies here they were feed large amounts of raw legumes or other foods containing lectins that were raw and sure enough these animals got very sick. But here’s where the disconnect lies: research suggests that a large amount of the lectins that are present in legumes is destroyed by heat in cooking, therefore when you cook the beans the lectins are almost completely destroyed. These are also disabled because they bind to sugars as the carbohydrates are broken down. In the case of the lectins, these bind to the sugars (or carbohydrate) in the beans and they are not going to be absorbed in the blood stream. The argument not to eat them kind of falls flat, given that most people wouldn’t consume raw beans! Peanut lectins are the exception and most people eat peanuts and peanut butter raw so there is a basis for caution there (i.e. don’t consume an entire jar in one go). With all of that in mind, there is limited research that has been conducted in humans to test this theory. But if you are cooking beans in a normal way, and if you are soaking them first – which is always recommended (soaked overnight) then you are able to disable the lectins first and then any residual lectins are combined with the sugars in the beans, which prevents us from absorbing them. Therefore the beans aren’t toxic and they are not going to kill you.
So why not eat beans? They are not as nutrient dense compared to other paleo protein sources. In addition, beans and legumes do contain carbohydrate types that are problematic for some people – these are known as FODMAPS. These cause digestive distress and people with fructose intolerance or small intestinal bacterial overgrowth will be best to avoid these. So digestive problems related to legumes might very well be (and mechanistically it makes more sense) that FODMAPS are causing the problem. That said, if you can’t tolerate legumes then it is best to avoid them.
Research also indicates that legumes can, over and above other foods, cause a larger insulin response in people who already have some glucose intolerance or impairment. Work currently being analysed by Catherine Crofts, a PhD student in our research centre suggests that people who are metabolically disregulated are able to clear the subsequent carbohydrate from their blood stream, but have an inappropriately high insulin response when they are tracked for up to five hours after consuming legumes. Our understanding of insulin and blood sugar is expanding to recognise that, along with high blood sugar levels, hyperinsuleniamia is as toxic to your body. This can lead to leptin resistance (your body is unable to read signals from leptin that is released when we’ve had enough to eat), inflammation, and other associated issues. This is another group that would be better off not eating legumes. In addition, if you re following a lower carbohydrate, high fat diet, you need to be mindful of the carbohydrate content of legumes – these are rich in carbohydrate – perfect as the carbohydrate component of a meal perhaps, but not if you are monitoring your intake, and not as a regular replacement for animal protein if you’re trying to maximise nutrient intake.
For the vegetarians who happily consume these on a daily basis and their main roadblock to investigating a paleo approach to diet, hopefully this highlights that it really is just a wholefood diet. For other healthy individuals that would like more variety, then there is no reason to exclude them if they also are relatively healthy. Many paleo advocates have changed their stance on legumes as more information comes to light, and this makes sense given that the overall premise is to advocate the most nutrient dense diet that you can eat. Legumes can and do have a role – and this might differ from your understanding of the paleo diet.