Why you should eat whole-grain foods
Dr Haran Sivapalan
July 4, 2018
As part of a series of articles unveiling the science behind your Personal Insights and Actions, we look at the research behind your optimal whole-grain intake. Is cracked wheat all it's cracked up to be? Is brown rice better for you than white rice? Just how much whole-grain should you be eating?
What are whole-grains?
The term ‘grains' refers to the seeds of cereal plants such as wheat, oats, barley, rye, and rice.
‘Whole-grains' are so-called because they refer to the entire grain, which comprises three parts:
- Bran – this is the outer layer of the grain and is rich in fiber, B vitamins, iron, magnesium, and zinc.
- Endosperm – this forms the bulk (around 80%) of the grain and acts as an energy store for the seed. Given this purpose, the endosperm is also a good source of carbohydrate and protein.
- Germ – the innermost embryo of the grain. It contains Vitamin E and some B vitamins.
Unlike whole-grains, refined grains do not possess a bran or germ layer. This is because the milling process removes these layers, consequently denuding the grain of fiber and nutrients.
What are examples of whole-grain foods?
There are plenty of healthy sources of whole-grains, which can be eaten both as snacks and as part of a main meal. Wholemeal bread, barley, brown rice, oats and whole-grain breakfast cereals are all widely available in supermarkets. Buckwheat, quinoa, bulgur wheat and ‘ancient grains', such as Kamut, freekeh, and teff, are also excellent sources of whole-grains. A lot of these grains can be consumed in various forms, including bread, pasta, crackers, and popcorn.
What are the health benefits of whole-grain foods?
As reflected in the dietary guidelines of various government agencies, whole grains have well-established health benefits. The US FDA (Food and Drug Administration) currently recommends adults eat three 1-oz servings of whole-grains per day to maintain a healthy heart. In the UK, the NHS (National Health Service) advises diabetic individuals to opt for whole-grain sources of carbohydrate for better control of blood glucose levels.
These recommendations are supported by several studies linking whole-grain consumption to numerous health benefits including a lower risk of cardiovascular disease, type 2 diabetes and cancer, improved insulin function, and better blood lipid profiles.
In this vein, a 2016 meta-analysis published in the British Medical Journal, found that 90g of whole-grains per day (about three servings) was associated with a 21% lower risk of coronary heart disease and a 16% lower risk of other cardiovascular diseases. When it came to deaths related to Type 2 diabetes, three daily servings of whole-grains was associated with a 36% reduction in mortality rate.
By contrast, the above meta-analysis found little relationship between positive health outcomes and intake of refined grains, white rice, and total grain consumption. This strongly suggests that there's something special about whole-grains in particular. So, just what is the magic constituent of whole-grains?
Why are whole-grains good for you?
As previously mentioned, the bran part of whole grains (which is absent in refined grains) is rich in fiber. Fiber is thought to be mostly responsible for the beneficial effects of whole grain on digestive, metabolic, and cardiovascular health.
There are two main mechanisms by which fiber improves control of blood glucose levels, thereby cutting your risk of diabetes and cardiovascular disease.
Firstly, soluble fiber, which dissolves in water to form a gel-like substance in the digestive tract, can help delay the digestion and absorption of carbohydrates, preventing sharp spikes in blood glucose that are harmful to the body.
Secondly, fiber becomes fermented by gut bacteria in the intestines. This fermentation process produces molecules called short-chain fatty acids (SCFAs). In turn, SCFAs enter the circulation and find their way into fat, liver and muscle tissues, where they act as signaling molecules to enhance sensitivity to insulin.
SCFAs produced from fiber are also thought to improve blood lipid (fat) profiles. Specifically, it's believed that SCFAs inhibit your liver from producing cholesterol. On this note, a systematic review of the literature reported that eating whole grains lowers levels of blood triglycerides and ‘bad' LDL cholesterol by between 2 and 5%.
While this may sound inconsequential, studies suggest that a 1% cut in LDL cholesterol is associated with a 1% reduction in risk of cardiovascular disease. Clearly then, there is some veracity to the ‘heart-healthy whole grains' slogan that adorns the boxes of your breakfast cereals.
Can whole-grains help me to lose weight?
Another widely-touted claim of high-fiber, whole-grain breakfast cereals is that they'll keep you full until lunchtime. You'll resist that mid-morning temptation to reach for the cookie jar. A potential corollary of this is that whole grains will aid weight loss.
While studies are demonstrating that whole-grains, particularly oats, barley, and rye, can promote satiety (feelings of fullness), the evidence that this leads to weight loss is less convincing.
There is undoubtedly a correlation between eating more whole-grains and having a healthier BMI and body fat percentage. Alas, interventional studies, where subjects are put on a whole-grain-rich diet and compared to a control group, do not consistently show that whole-grain foods engender weight loss. It's important to note that this may merely be a reflection of the types of studies conducted to date, many of which have been performed over short time frames (less than 16 weeks).
Nevertheless, a systematic review of interventional studies did find that whole-grain diets can bring about a small but significant loss of body fat. So, although whole-grains are not a miracle weight loss seed, they can be included as part of a healthy diet and are less likely to lead to fat deposition compared to refined carbohydrates.
How do genes play a role?
On the current evidence, we all may reap benefits from consuming whole-grains. Other things being equal, our blood fat, blood sugar, and satiety levels may improve by incorporating more whole grains into our diet.
Individuals with gene variants which may impair fat and glucose metabolism, insulin function, and satiety arguably have a greater need to increase their whole-grain intake. Consonant with this, FitnessGenes accounts for several related genes including PPARG, IGF1, and FTO, when making your whole-grain Personal Insights and Actions.
How much whole-grain should I eat?
As with most things in nutritional science, this isn't a simple case of the more you eat, the better. Rather, the relationship between health benefits and whole grain consumption is non-linear. Going from eating no whole grains to eating up to 4 servings (a serving being 1oz/28 grams) cuts the risk of coronary heart disease, cardiovascular disease, and mortality from diabetes more dramatically. There is no harm in eating more than this amount, but the health benefits start to tail off.
In line with this research, we recommend that you eat at least 3-4 servings of whole grains per day. Depending on your genes and lifestyle, this advice may be particularly pertinent for you.