Humans didn’t evolve to eat a diet high in breakfast cereals, pasta, potato chips, and many of the other starchy foods that make up the typical Western diet. Rather, for most of human evolution, nutrient-dense plant foods rich in fiber and with a low-moderate carbohydrate density were the main sources of complex carbohydrates. This is something most people with an interest in ancestral health and nutrition are well aware of, and those who adhere to a Paleo-style diet often remove grains, fruit juices, and many other carbohydrate-heavy foods from their diet completely. But what should these foods be replaced with?
A lot of people who adopt a Paleolithic, hunter-gatherer style diet or another similar nutritional strategy end up replacing grains and other carb-heavy foods with plenty of fats, often dramatically reducing their carbohydrate consumption and boosting their intake of fatty foods such as grass-fed butter, avocados, coconut oil, and bacon. I know I was one of those people when I first started out with an ancestral diet a long time ago. This strategy definitely has its merit in certain situations, and for me personally it seemed to work pretty good, at least much better than what I had been doing previously. However, as you are undoubtedly aware if you’ve been following this blog, my stance on carbohydrate intake has evolved quite a bit since those early days. While I’m all for ditching all of the refined grains, sugar-laden beverages, and carb-heavy fruit juices and getting more healthy fats into the diet, going very low carb is rarely optimal.
It’s about finding a carbohydrate intake that fits your activity levels and goals – and perhaps most importantly, getting your carbs from the right types of foods. Sweet potatoes are a great option in that regard.
Sweet potatoes as part of traditional diets
In my 4-part series on carbohydrate intake I made the case that getting about 20-40% of the daily calories from carbohydrate is a good general guideline for most people. However, I also argued that while a high-carbohydrate diet isn’t necessarily optimal, it is certainly possible to thrive on diets that contain a lot more than 40% carbohydrate – particularly if the carbs come from fruits, roots, and tubers. This is clearly seen in studies which show that some non-westernized people are lean and fit and have very low rates of degenerative diseases “despite” eating a high-carbohydrate diet. These reports are particularly relevant to this post, as some of the healthiest populations that have ever been studied eat diets high in – yes, you guessed it – sweet potatoes (1). The sweet potato is an important food source for residents on the Ryukyu Island, the Maori people, and many indigenous populations in Central and South Americas, Africa, the Caribbean, Hawaii, and Papua New Guinea (2).
If you’ve followed this website or other ancestral health blogs, you’ve probably read about the diet and health of the Kitavans on the Island of Kitava and/or the Okinawans in Japan. Nonetheless, let’s do a quick run-down. Both of these non-westernized populations traditionally eat a diet that is very high in carbohydrate, and of particular importance to this post, they eat a lot of starchy root vegetables.
When Staffan Lindeberg and his colleagues visited the Island of Kitava, one of the Trobriand Islands in Papua New Guinea’s archipelago, in 1989, the residents on the island lived exclusively on root vegetables (yam, sweet potato, taro, tapioca), fruit (banana, papaya, pineapple, mango, guava, water melon, pumpkin), vegetables, fish and coconuts. As anyone who’s familiar with the research on ancestral diets know, the kitavans exhibited superb health markers and had very low prevalence of overweight and chronic degenerative disease. Starchy foods such as sweet potatoes were an important part of their diet, with 69% of their calories coming from carbohydrates. Other non-industrial people on Papua New Guinea have been known to eat diets that are even higher in carbohydrate than this, with sweet potatoes accounting for more than 90% of the total food intake (3).
Okay, what about the Okinawans? Traditional people from the Ryukyu Islands (of which Okinawa is the largest) are known for their long average life expectancy, high numbers of centenarians, and low mortality from cardiovascular disease, cancers, and other age-associated disease (4, 5, 6). The traditional diet in Okinawa is high in root vegetables, green and yellow vegetables, soybean-based foods, and medicinal plants, and contain small-moderate amounts of marine foods, lean meats, fruit, medicinal garnishes and spices, tea, and alcohol (5). As for sweet potatoes specifically, detailed population surveys of the traditional Okinawan diet in 1949 found that the daily intake of this starchy, tuberous root exceeded 800 grams (!!) (4). Of the 1785 calories they consumed daily, 69% came from sweet potatoes (4). Carbohydrate was by far the most dominant macronutrient in the diet, accounting for approximately 85% of the total calories consumed (4). Their traditional low-calorie, nutrient-dense diet was widely practiced on the island until about the 1960s, but over the last several decades, dietary practices have been shifting towards Western and Japanese patterns, with fat intake rising and the sweet potato increasingly being replaced by rice and other cereals (4).
Clearly, in itself, the fact that some healthy traditional societies eat diets high in sweet potatoes doesn’t necessarily mean that eating a lot of sweet potatoes is the way to go for good health, as there are certainly a wide range of factors that could help explain the low prevalence of chronic disease and/or the high longevity of these traditional people. Take the Okinawans for example; several factors (e.g., their low energy intake, high intake of phytochemicals) likely contribute to their long average life expectancy and low mortality from age-related diseases. Also, needless to say, I don’t think anyone looking to achieve optimal health should up their intake of sweet potatoes so it matches that of the traditional Okinawans. Nonetheless, the fact that sweet potatoes make up the foundation of the diet of some of the healthiest (low rates of degenerative disease, not necessarily infectious disease) populations that have every been studied clearly suggest that it’s a food that, at the very least, can safely be eaten as part of a healthy diet.
From an evolutionary perspective, it’s safe to say that roots and tubers have been a part of our diet for a long time. There’s solid evidence to suggest that Underground Storage Organs (USOs) were regularly consumed by our preagricultural ancestors, often serving as important fallback food for when meat and other preferred foods weren’t available (7, 8). Many contemporary hunter-gatherer societies (e.g., the Hadza) eat plenty of tubers, particularly during parts of the year when they don’t get a lot of meat, honey, and other foods that tend to be preferred over the less calorie dense and “duller” USOs.
6 nutritional benefits of sweet potatoes
- Sweet potatoes are particularly high in beta-carotene, an organic compound with antioxidant properties that is responsible for giving sweet potatoes their orange/red pigment. Consuming more beta-carotene rich foods can help give you a slight “tan” and healthier look, as beta-carotene contributes to the yellow pigment found in human skin (9, 10). Also, its deposition in the skin is thought to contribute to photoprotection, meaning that it can help guard you against the deleterious effects of both natural and artificial UV light exposure, and raise the minimum amount of UVR exposure required to cause a sunburn (9).
- Sweet potatoes are a good source of complex carbohydrates, antioxidants, and dietary fiber.
- Sweet potatoes are nutrient-dense, containing particularly high amounts of beta-carotene.
- Sweet potatoes are low in antinutrients.
- Sweet potato extract has anti-obesity and anti-inflammatory potential (in vitro) (11)
- Sweet potato protein exerts anticancer effects on human colorectal cancer cell lines, both in vitro and in vivo (12).
Are the sweet potatoes you find at your grocery store similar to those consumed by traditional societies?
Perhaps needless to say, the types of foods we’re eating and the way our food is produced, prepared, and processed have changed dramatically over the past millenia. As for fruits and vegetables, a general theme is that uncultivated versions tend to be markedly more fibrous and lower in sugar and starch than domesticated varieties (13). In other words, the sweet potatoes you pick up at the grocery store down the block might be very different from the ones that were consumed by a healthy resident on the Island of Kitava. As Dr. Stephan Guyenet says: “Sweet potatoes aren’t necessarily sweet. Caribbean ‘boniato’ sweet potatoes are dry, starchy and off-white. In the US, I prefer the yellow sweet potatoes to the orange variety of sweet potato labeled ‘yams’, because the former are starchier and less sweet” (3).
What does this mean? Should you avoid those delicious sweet potatoes after all? No. If we had to remove all of the foods from our diet that were markedly different from those consumed by our hunter-gatherer ancestors and non-westernized traditional populations, there wouldn’t be much left. However, I belive it’s important to keep these things in mind when we plan our diet, go out shopping (I prefer organic sweet potatoes), and cook our food (Cooking method affects the glycemic index of sweet potatoes, among other things).
How to incorporate sweet potatoes into your diet
As I explained in the beginning, I believe getting about 20-40% of the daily calories from carbohydrate is a good general guideline for most people, with Paleo-approved foods such as roots, tubers, and some fruit being the dominant sources. How much sweet potato you should eat largely depends on what type of diet you’re currently consuming, your activity levels, and your current health status. Some people, such as those with an intense sweet tooth or those who are severely overweight and insulin resistant, may not do so well with a lot of sweet potatoes.
However, if you’re someone who’s looking for a good source of carbohydrates to fuel your training, sweet potatoes are an excellent option. The actual amount you’ll be eating clearly depends on the types of activities you’re performing and how active you are. Personally, I primarily perform strength training, sprinting, and low-level activities such as walking, and I find that 75-175 grams of carbohydrate/day (excl. fiber) tends to be enough. Someone who performs a lot of high-intensity endurance work will clearly need a lot more.
Needless to say, if you’re already eating a lot of rice, wheat, pasta, and other similar foods with a very high carbohydrate density – and have no intention or desire to take these foods out of your diet, adding even more starch from sweet potatoes is certainly not going to help your situation. But, if you’re looking for a better carb-option and are willing to make some changes to your diet, replacing these foods with sweet potatoes is certainly a good way to go.
If you’re someone who eats a very low-carb diet and is under the impression that you can almost eat as much fat you want as long as you limit your intake of carbohydrate, you’ll probably benefit from re-evaluating your perspective on healthy nutrition and making some adjustments to your diet. From an evolutionary perspective, a diet that is very high in butter, cheese, oils, bacon, and other similar foods with a very high fat density is a novelty, and as I explained in my comprehensive article on saturated fat, there are many problems associated with such a diet. My two cents: Choose a more balanced approach, and replace some of your fatty foods with healthy plant foods such as sweet potatoes.
Now I want to hear from you: Do you regularly eat sweet potatoes? Are you going to add more of this starchy root into your diet after reading this?
Picture 1: Creative commons picture by David Lifson. Some rights reserved.
Picture 2: The Okinawa Centenarian Study.