The Scientific Lowdown on Low-Carb
It can be difficult to tease out the truth about carbs. One minute they are healthy. The next minute they are killing us. Today the internet is telling us we can’t live without them. Low-carb diets are trending within fitness Facebook groups and promise us weight loss. But the only healthy diet is a sustainable, balanced one with good sources of dietary fiber, fruits and vegetables — which means carbs. Science says: eat moderate levels of high-quality, low glycemic index, plant-based carbs.
Carbohydrates, or carbs, are a large group of organic compounds including sugars, starch and cellulose that occur in both our foods and our tissues. Chemically, carbohydrates contain hydrogen and oxygen in the same ratio as water (2:1) and can be broken down inside of our bodies to release energy. In our daily lives, however, carbs are often synonymous with simple dietary carbohydrates and starches including bread, pasta and refined sugar.
“In practice, dietary carbohydrates comprise compounds that can be digested or metabolically transformed directly into glucose, or that undergo oxidation into pyruvate, including some sugar alcohols (eg, sorbitol).” — Dietary Carbohydrates, BMJ 2018
Carbs get a bad rap. As a society we’ve long vilified dietary fats and cholesterol, but carbohydrates have quickly become the scapegoat for Americans’ heart problems, obesity, diabetes and even cancer. This isn’t without reason — simple carbohydrates and added sugars can wreak havoc on body and brain. Cancer cells generally love sugar (but then some cancer cells like to use fats for fuel, too). Low-carb diets have been associated with more rapid weight loss than other diets, even if the returns diminish over time (especially as very low-carb diets are extremely difficult to maintain for life).
But the real story of how carbs affect our health and longevity is, as always, more complicated.
More Reading: Food for Thought at the BMJ
Physicians and nutritionists often cringe at the mention of paleo and keto diets. This isn’t because these diets don’t have intrinsic benefits (in fact, diets that promote a state of ketosis in the body can have benefits especially for people prone to brain injury and people with inflammatory disorders), but because eliminating carbs doesn’t necessarily mean eating healthy - at all. There is a reason why the Dietary Guidelines for Americans recommends that carbohydrates make up 45% to 65% of your daily calories. Many sources of the nutrients and dietary fibers important to our health are also sources of carbs — fruits and vegetables, legumes and whole grains.
Food sources of dietary fiber
- High fiber bran cereal: 9–14 grams per serving
- Navy beans: 9–10 grams per serving
- Chickpeas: 8 grams per serving
- Artichoke: 7 grams per serving
- Pears, raw: 5–6 grams per serving
- Pumpkins seeds: 5 grams per serving
- Apple: 4–5 grams per serving
- Green peas: 3–5 grams per serving
- Chia seeks: 4 grams per serving
- Blackberries: 3 grams per serving
- Sweet potato: 3–4 grams per serving
- Almonds: 3–4 grams per serving
A study published in The Lancet this week finds that “the epidemiological association between carbohydrate intake and death is U-shaped, with the lowest risk occurring with a carbohydrate intake of 50–55% of energy, and with both lower and higher intakes being associated with higher risk of death,” (Mente & Yusuf, 2018). A diet where approximately half of your calories come from carbs looks a lot like other “longevity” diets — fruits, vegetables, legumes, whole grains, nuts, fish, dairy and unprocessed, lean meats, all in moderation.
In 2016, researchers in Italy studied the dietary habits, fasting lipid levels, blood sugar control and inflammation markers of over 1,700 people with type 2 diabetes. Individuals who get a lot of fiber in their diets, from complex carbohydrates and vegetables for example, tended to have better plasma lipid profiles, better blood sugar control and lower levels of inflammation biomarkers such as C-reactive protein. Added sugars and fats had the opposite effect. It’s important to make the distinction between high carb diets that include a lot of simple carbohydrates, and high carb diets that include lots of slowly absorbable, low glycemic index carbohydrates.
“In people with type 2 diabetes, variations in the proportion of fat and carbohydrates of the diet, within the relatively narrow ranges recommended by different nutritional guidelines, significantly impact on the metabolic profile and markers of low-grade inflammation. The data support the potential for reducing the intake of fat and added sugars, preferring complex, slowly absorbable, carbohydrates.” — The TOSCA.IT Study, 2016
Good Carb, Bad Carb
As the scientific community reminded us this week with the publishing of the meta-analysis of dietary carbohydrate intake and mortality in The Lancet, carbs are neither bad nor good. (The same can be said for fats — plant fats have far different effects on our body than animal fats do).
Both low carb and high carb diets can be healthspan boosting. Low carb diets can be either healthy or unhealthy depending on what foods are used to substitute those carbs. And when it comes to high carb diets, those can be healthy too because, well, not all carbs are created equal.
“Low carbohydrate dietary patterns favouring animal-derived protein and fat sources, from sources such as lamb, beef, pork, and chicken, were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality, suggesting that the source of food notably modifies the association between carbohydrate intake and mortality.” — Seidelmann et al. 2018
More important than whether your normal diet is low carb or high carb (or more ideally, moderate carb!) is how often you consume a mix of food groups associated with metabolic health. Whole grains, vegetables and fruits are key components of most diets associated with longevity. These food groups, not incidentally, as also associated with lower levels of inflammation.
Chronic inflammation can be triggered by environmental and lifestyle factors such as smoking, depression, infection and a poor diet. We’ve long known that a Mediterranean diet, full of unsaturated plant oils, whole grains and antioxidants from fruits and vegetables, is linked with lowered levels of inflammation, while the Western diet, stereotypically full of processed and “fast” foods, is associated with increased inflammation, cardiovascular disease incidence and obesity. Obesity, in turn, breeds more inflammation and metabolic inflexibility.
A Veggie a Day to Keep the Inflammation at Bay
There is mounting evidence that plant-based foods, especially unprocessed vegetables and fruits, have beneficial anti-inflammatory effects on the body. Foods with added sugars, simple carbohydrates and refined grains typically have the opposite effect. Plant-derived compounds such as flavonoids work as antioxidants and anti-inflammatory agents.
Why do we care about inflammation in the body? Because chronic inflammation, which our diets could be making worse depending on what we eat, has been linked to the early onset and development of diseases that are also unsurprisingly known as diseases of aging: arteriosclerosis, obesity, diabetes, neurodegenerative diseases and cancer.
You might not realize it, but eating a meal triggers inflammation in your body, at least temporarily. Individuals with food allergies and diabetes know what this feels like on an exaggerated level. Eating a meal causes a temporary spike in your blood sugar and lipid levels that can increase levels of oxidative stress or reactive oxygen species in and around your cells. Thankfully if you are healthy, eat well and exercise, your body quickly gets to work cleaning up these reactive oxygen species (eating antioxidants can help!). But if you have diabetes or you are constantly flooding your body with simple sugars, your body will react with elevated levels of reactive oxygen species that lead to inflammation.
“Markers of inflammation, a well-recognized manifestation of oxidative stress, have also been observed to increase in response to intermittent elevated glucose levels.” — Oxidative stress in type 2 diabetes: the role of fasting and postprandial glycaemia
The good news is that there are ways to curb meal-induced oxidative stress so that you don’t end up with harmful, chronic inflammation. You can help slow the digestion of your meals and avoid elevating your blood sugar to harmful levels by eating a mix of food groups. Be sure to include good sources of fiber and antioxidants. Physical activity (consider a post-meal walk) also improves inflammation by lowering post-meal glucose.
Low glycemic index vegetables and fruits, nuts, lean protein, vinegar, tea, fish oil, calorie restriction, weight loss, and moderate- to low-dose alcohol each significantly improve post-meal inflammation. — Dietary Strategies for Improving Post-Prandial Glucose, Lipids, Inflammation, and Cardiovascular Health
“At the level of bioactive compounds occurring in plant foods, primarily carotenoids and flavonoids seem to modulate inflammatory as well as immunological processes. […] By means of anti-inflammatory activities a plant-based diet may contribute to the lower risk of cardiovascular diseases and cancer. A high intake of vegetables, fruit, and whole wheat as recommended by all international nutrition authorities provides a wide spectrum of bioactive compounds at health-promoting concentrations.” — Watzl, 2013
But doesn’t fruit have a lot of sugar in it?
Whole fruits are high in fiber, vitamins, minerals and antioxidants, and most actually have a moderate to low glycemic index. Regular consumption of fruits, especially blueberries, apples and grapes, “is associated with lower risk of type 2 diabetes, cardiovascular disease, cancer, and all-cause mortality in prospective cohort studies.” Avoid sugary fruit jams and juices though — those have low or no fiber content and are associated with an increased risk of diabetes.
Foods That May Lower Inflammation and Post-Meal Reactive Oxygen Species
- Strawberries — their anthocyanins can decrease levels of pro-inflammatory cytokines in the body.
- Green tea — “Green tea consumption over short and long periods appears to ameliorate endothelial dysfunction by scavenging free radicals with anti-inflammatory and anti-apoptotic properties in healthy male smokers.” — Oyama et al. 2010
- Almonds and pistachios — these nuts consumed with a meal can slow digestion.
- Olive oil
- Broccoli — a compound in this vegetable, called sulforaphane, alleviates neuroinflammation in mice.
- Foods high in dietary fibers
- High quality protein — lean protein will curb post-meal sugar spikes and improve satiety.
- Whole grains — that’s right, complex carbs can actually improve post-meal glucose and insulin balance.
Fasting to Curb Those Carbs
One person on a high carb diet may be metabolically healthier than another person on the same diet, as a result of other lifestyle factors including how often that person exercises, how much they eat and even when they eat.
Intermittent fasting (you may know it as one of our favorite healthspan practices here at LifeOmic!) has anti-inflammatory effects. Intermittent fasting has been shown to help the cells in our bodies switch, if just for a short time, from a “growth” state to a more energy conserving state. Fasting helps the body switch from a state of burning readily available sugars to a state of burning harder-to-access fats, and suppresses nutrient signaling pathways.
This metabolic switching leads to a reduction in the reactive oxygen species that can damage our cells and DNA, a healthy level of cellular “self-eating” and even suppression or killing of senescent “zombie” cells. Intermittent fasting can improve cell and tissue function, including the function of immune system cells involved in inflammatory responses.
Unfortunately, the anti-inflammatory effects of intermittent fasting don’t last, especially if we break our fasts with inflammatory foods. There’s evidence that in the treatment of diseases such as rheumatoid arthritis, intermittent fasting interventions are much more effective when followed by a vegetarian or equivalent plant-based diet. But regularly intermittent fasting may still help dampen inflammation induced by diet and other lifestyle factors, particularly as regular fasting is associated with greater insulin sensitivity.
“Major factors implicated in aging whose generation are accelerated by gluttonous lifestyles and slowed by energy restriction in humans include the following: (1) oxidative damage to proteins, DNA, and lipids; (2) inflammation; (3) accumulation of dysfunctional proteins and organelles; and (4) elevated glucose, insulin, and IGF-I, although IGF-1 decreases with aging and its severe deficiency can be associated with certain pathologies (Bishop et al., 2010, Fontana and Klein, 2007). Serum markers of oxidative damage and inflammation, as well as clinical symptoms, are reduced over a period of 2–4 weeks in asthma patients maintained on an alternate day fasting diet (Johnson et al., 2007).” — Fasting: Molecular Mechanisms and Clinical Applications, 2014
If you love and simply can’t do without carbs, you can help curb the negative impacts of consuming these foods by exercising, eating these foods earlier in the day (you are more insulin resistant or vulnerable to sugar overloads at night) and practicing time-restricted feeding or intermittent fasting on a regular basis.
