Let's first get down to the specifics. The DASH diet outlines the following recommended servings:
Food and Servings
- Grains and grain products: 7 to 8 a day (e.g. 1 slice bread, half a cup dry cereal, half a cup cooked rice, pasta, or cereal)
- Vegetables: 4 to 5 a day (e.g. 1 cup raw leafy vegetable, half a cup cooked vegetable, three quarter cup vegetable juice
- Fruits: 4 to 5 a day (e.g. three quarter cup fruit juice, 1 medium fruit, one quarter cup dried fruit, one half cup fresh, frozen, or canned fruit)
- Low-fat or non-fat dairy food: 2 to 3 a day (e.g. 1 cup skim or 1% milk, 1 cup low-fat yogurt, 1 and a half oz. part-skim or non-fat cheese)
- Meats, poultry, & fish: 2 or less a day (3 oz. broiled or roasted lean meats, skinless poultry, or fish)
- Nuts, seeds, & beans: 4 to 5 a week (e.g. one third cup nuts, 2 Tbs. sunflower seeds, half cup cooked beans )
- Added fats, oils, & salad dressing: 2 to 3 a day (e.g. 1 tsp. oil or soft margarine, 1 tsp. regular mayonnaise, 1 Tbs. low-fat mayonnaise, 1 Tbs. regular salad dressing, 2 Tbs. light salad dressing)
- Snacks & sweets: 5 a week (e.g. 1 medium fruit, 1 cup low-fat yogurt, half cup low-fat frozen yogurt, three quarter cup pretzels, 1 Tbs. maple syrup, sugar, jelly, or jam, half cup Jell-O, 3 pieces hard candy, 15 jellybeans)
So given the current trend of low-carb dieting, the 7 to 8 servings of grain and grain products is likely the most controversial. The low-carb craze really is variations on a theme. So you get Atkins, the ketogenic diet, the Paleo diet, etc., but they all focus on one thing: reducing or nearly eliminating (at least restricting) "carbs."
From a physiological perspective, it is understood that the body runs on glucose and glycogen as an energy source, which are carbs in themselves. But there is a difference between dietary carbs and biological carbs, I grant you that. But the fact remains, the body will find its carbs regardless, and it prefers glucose as its prime source, followed by glycogen, then fat, then muscle.
From an anthropological perspective, there is evidence that a fair portion of the Paleolithic diet consisted of carbs. There is evidence of tubers being a part of the diet. The challenge for many years is that humans didn't often have the benefit of established long-term settlements, and so secure food sourcing was an issue. It's no surprise that grains, legumes, and even tubers weren't a prominent feature.
However, there is mounting evidence that grains were a part of ancient diets. Have a look:
Figures and Tables : Processing of wild cereal grains in the Upper Palaeolithic revealed by starch grain analysis : Nature
Harvard Gazette: Researchers find earliest known oven
Observations: Humans feasting on grains for at least 100,000 years
From an evolutionary standpoint, humans are expert generalists. We're not carnivores; we're not herbivores; we're omnivores. We're highly adaptable and there is also evidence of this. The challenge remains, however, of finding enough evidence of food-related matters of such periods, considering how long ago they were.
That said, I don't think the consumption of legumes and grains is inherently bad. I don't think the consumption of most food is inherently bad. Food, generally, is a source of energy and nutrients, and so we must look at the balance of such energy and nutrients. Grain contains nutritional material
unique to grains. Some of this material is
unique to specific grains. Some of these are antioxidants and phytonutrients found to have great benefit to heart health, colon health, etc., and are found in such things as oats and buckwheat, which, in my opinion, are nutritional powerhouses.
But whole grains are
whole grains: the endosperm, the germ, the bran—the whole kit and kaboodle. If I'm not mistaken, the majority of grain products consumed in North America are refined, which means that the germ and bran are removed, while the endosperm is mashed into fine white flour. Between the germ and bran, this removes important essential fatty acids, vitamin E, fibre, phytonutrients, B-vitamins, and a wide array of trace minerals. White flour is grain made impotent.
That's the problem.
The human body is designed to take advantage of a wide array of foods, and it thrives on being able to benefit from this array. Reducing the array can introduce problems of imbalance. Will, you mentioned fibre. While fruit and vegetables have fibre, grains have a counterbalance of fibre that helps ensure we get enough of both soluble and insoluble fibre.
Before I get too long-winded here, I will say outright that grains aren't bad for you, nor do you have to severely restrict them to be healthy. Grains contain vitamins, minerals, essential fatty acids, complex carbohydrates, protein, and fibre, often in good supply. They are a great source of nutrition. Some, such as oats, actually
help with the insulin response, despite what people might think.
The problem isn't grain; the problem isn't carbs. The problem is too much over-processed grains and over-processed food in general. The problem is too much bad fat, and not enough good fat. (Omega-3s anyone?)
Singling out one or two aspects of our diet (whether it's a macronutrient or an entire food group) I think does more to distract from the greater issue: not enough of us eat wholesome foods; not enough of us balance our diets. We eat too much refined grains and sugar. We eat too much salt, etc.
We can say that "diet" is a dirty word and is a concept that sets people up for failure, but diet is diet regardless: it's what we eat. North Americans clearly need guidance, and I would argue that if more North Americans were instructed on how to follow the DASH diet, obesity would be less epidemicky.