Carbohydrates are our bodies main source of fuel, and put simply, carbohydrate restriction is limiting the amount of carbohydrates present in the diet. Carbohydrates include a range of foods from fruits and vegetables to whole and processed grains. Dairy, table sugar, starches—they’re all part of the carbohydrate family.
When you consume a meal, macronutrients are broken down into their component parts for use by the body. In the case of carbohydrates, digestion begins in the mouth and continues until the food is broken into its monosaccharide units.
Get a quick refresher on. how carbs break down and what differentiate “good” carbs from “bad”.
Carb restriction isn’t a new concept. It’s often used in medical nutrition therapy to treat a variety of conditions from diabetes, to cancer, to epilepsy. But will carb restriction help you live longer? As in all things longevity, definitive answers are scarce but carb restriction might just be the single greatest tool you can use for increasing your number of healthy years.
Standard vs. Carb Restricted Diet Patterns
Every diet pattern includes a ratio of macronutrients. Standard diets follow the acceptable macronutrient distribution ranges (AMDR) and are composed of 45-65% carbs, 10-30% protein and 20-35% fat. Carb restriction drastically reduces the proportion of carbohydrates included in the diet, although no standard ranges exist for carb restriction. And different levels of restriction will affect people quite differently.
Since carb restriction lies on a spectrum, we can generalize by segmenting it into three clear categories of diets:
- Very low-carbohydrate—less than 10% carbs (e.g., ketogenic diet)
- Low-carbohydrate—11-26% carbs (e.g., Atkins diet, Phase 1 South Beach diet)
- Moderate-carbohydrate—26-44% carbs (e.g., Phase 2 South beach diet)
As with macronutrient ratios, the types of foods acceptable for very low-carb, low-carb, and moderate-carb diets vary. Very low-carb diets like keto excludehigh-carb foods like starchy fruits and vegetables, grains, and sugar and increase foods that are high in fat like nuts, cream, and butter. Keeping a strict Keto diet can be quite challenging and over the long-term can carry risk of some negative effects (e.g. increased LDL or triglycerides levels). However, periodically restricting carbs to keto diet levels can help our bodies get used to burn fat for fuel and thereby increase our metabolic flexibility.
Very low-carb diets also shift the balance of fats from long-chain triglycerides to medium- and short-chain triglycerides that are easier to digest and readily absorbed from the gut. Low-carb diets like Atkins or Phase 1 of the South Beach diet exclude high-carb foods like bread and pasta in favor of non-starchy vegetables and higher dietary ratios of protein and fat, most of which are derived from animal products.
Finally, moderate-carb diets represent the most flexible of the three categories but limit high-carb foods like pasta, bread, starch, and sugar and favor non-starchy vegetables, low glycemic index (“GI”) fruits, beans, nuts, seeds, and higher ratios of protein and fat.
Health Benefits of Carb Restriction
Carb restriction can be practiced by all. For some of us, significantly restricting carbs may give us more energy, make us less tired during the day and eat less. For others our ideal might be to cut out breads, pastas, and processed grains. Regardless of where you fall, slowly getting used to slightly less carbs can have a positive and lasting effect on your long-term health.
In clinical settings, ketogenic diets have been successfully used in the treatment of epilespy, giving the patients greate seizure control (see study 1, study 2). Keto diets are also being increasingly recommended as part of standard care practices of diabetic and pre-diabetic patients among hospital dieticians.
Perhaps the greatest benefit of adapting to a carb-restricted diet is the eliminating of the worse carbs of all: those packed into highly processed foods with refined flours and sugars. These products have been linked with inflammation and chronic disease and are clearly a key driver behind the explosion of obesity as a health issue in many countries.
Perhaps one of the greatest benefits, and thus one the greatest selling features, of carb restricted diets is their effect on blood sugar and body weight. Therapeutically, carb restriction is among standard practice for preventive care teams looking after patients with diabetes and/or obesity. Because carb restriction drastically reduces high GI foods and replaces them with low GI foods, blood sugar (and thus insulin) doesn’t spike and remains stable as sugar is slowly released to the bloodstream.
Source: Harvard Health Publishing
Carb restriction also includes many high fiber fruits and vegetables which take longer to digest than processed foods and have a lower caloric (energy) density. This promotes satiety and can help individuals lose weight over time even if they find themselves eating more often. For example, assuming a standard calorie allowance of 2,000 kcal/day, an individual will consume more food eating low GI carbs with a low energy density than high GI carbs with a high energy density.
Check out this diagram to help visualize how carb-restriction shifts the energy balance in the diet and allows you to eat a greater volume without extra calories.
Avoid living in the extremes
While carb restriction isn’t a dangerous practice in itself, very-low carb diets and low-carb diets present their own risks. Case reports and anecdotes suggest that these two diet patterns can result in constipation, low blood sugar, lethargy, and irritability among patients. There are also reports of low-grade acidosis (increase in blood acidity) in patients adhering to ketogenic diets.
Altering nutrient ratios also poses the potential risk for nutrient deficiencies, particularly in regard to some B-complex vitamins (i.e., thiamin, riboflavin, niacin) that are largely derived from fortified grains and cereals in this country. Ketogenic diets have also been shown to raise blood lipids by as much as 30% (due to the increase in dietary saturated fat) and this review of 17 studies suggests a link between low-carb diets and all-cause mortality such that individuals with the lowest carb intake have a 31% increase risk of death from any cause.
There is also the issue of sustainability and dietary adherence long term. Due to the restrictive nature of these diet patterns, adherence is low. For this reason, it might be more sustainable long term to adopt a moderate-carb diet that allows a level of flexibility absent in very-low and low-carb diets. If you can combine this with periodically switching to a keto routine for a couple of weeks, you can try to get the best of both worlds.
Links to Longevity
One of the companies pioneering the potential links between carb restriction and longevity is Virta Health, an innovative health platform that’s taken the therapeutic concept of carb restriction and has applied it to diabetes management at scale.
In healthy individuals, blood sugar is regulated by hormones produced in the pancreas to keep blood sugars stable. One of the hallmarks of aging is dysfunction in nutrient signaling pathways that regulate glucose homeostasis. As our ability to regulate our sugar levels decreases, it negatively affects our whole-body energy metabolism and ultimately increases our overall susceptibility to disease.
Although the science on the exact mechanism creating insulin-resistance and disrupting glucose homeostasis is still evolving, lifestyle factors such as poor dietary habits, lack of exercise, heart disease, and obesity are well-established risk factors. (It is probably not coincidental that Metformin, a common drug used to treat diabetes, has been shown to have life-extending effects in both mice and people).
What Virta Health has shown through their study is that through lifestyle management --specifically carb restriction-- you have a very powerful tool for stabilizing blood sugar in diabetics, ameliorating increasing insulin resistance. The Virta protocol uses a remote care model to connect patients with health coaches who provide nutrition support and behavior change strategies. The initial nutrition guidance recommends that patients restrict dietary carbs to fewer than 30 g per day (less than 10% of intake), shifting the balance of macronutrients ratios in favor of proteins and fats. Patients are monitored by staff doctors who take measurements of biomarkers and manage medications on the way to achieving glycemic control.
Virta boasts some incredible results. Their recently published clinical trial (N=96) of pre-diabetics saw only 3% of patients go on to develop full blown type 2 diabetes after 2-years. Furthermore, 52% of patients adhering to the Virta protocol achieved a normal HbA1C at 2-years follow-up. Prevalence of diabetic/pre-diabetic co-morbidities like metabolic syndrome, fatty liver, and obesity also decreased during the trial period.
Virta’s results present some of the strongest findings in favor of carb restriction to manage diabetes but don’t occur in isolation. The Diabetes Prevention Program (DPP) and ongoing DPP Outcomes Study (DPPOS), both sponsored by National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), provide similar results as do these articles (study 1, study 2).
Go deeper: Click here to check out a list of Virta Health’s published research.
While Virta’s focus is on diabetes care, abnormal blood sugar doesn’t just occur in diabetics. This article suggests an aging component to blood glucose control. In fact, for every decade of life fasting and random plasma glucose levels increased by 0.15 mmol/L while 2-hour postprandial plasma glucose level increases by 0.26 mmol/L. These may seem like inconsequential elevations but in diabetes care, decimal increases can be the difference between normal and abnormal test results and influence the level of risk posed to a patient for other age-related illnesses. For instance, abnormal blood sugar carries a 32% increase in risk for cancer and markedly increases risks for dementia and cognitive decline. In fact, this study showed that abnormal blood sugar increased the risk of dementia by 73%!
Diabetes represents one chronic disease in a trifecta of adverse health outcomes. As co-morbidities go, if diabetes is present it’s likely that obesity and/or CVD is as well and if they aren’t, they are sure to follow if the disease isn’t brought under control. In that respect, carb restriction also proves helpful because reduced carb consumption isassociated with lower rates of obesity. Obesity has long been associated with an increased risk of cancer and CVD, but reducing carbs reduces body weight and that in turn decreases the risk of cancer, heart attack, and stroke.
There’s also evidence in the literature that carb restricted eating links with all-cause mortality but that the risk of death is mediated by what type of foods replace carbs in the diet. This prospective cohort study and meta-analysis of 15,428 adults assessed percentage of energy from carbohydrate intake and all-cause mortalityas well as whether substituting animal or plant sources of fat and protein for carbohydrates affected mortality risk over a period of 25 years. Following statistical analysis, results showed that the risk of death occurs along a u-shaped curve, such that individuals who have very-low carb intake as well as individuals who have very high carb intake are at the greatest risk for death from any cause.
Individuals who fall in the middle of the curve, particularly those with a median intake of 50-55% carb had the lowest risk of death. When study authors examined the curve taking into account what types of food replaced the carbs in the diet, individuals who replaced carb intake with animal protein and fat increased their risk of death by 18% while individuals who replaced carbs with plant proteins and fats reduced their risk of death.
Authors suggest that “[low carbohydrate diets with low plant and increased animal protein and fat consumption may stimulate inflammatory pathways, biological aging, and oxidative stress]” which can damage DNA and accelerate the hallmarks of aging. Conversely, substituting plant proteins and fats for carbs may be health protective due to the increase in fiber, phytochemicals, and other antioxidants which decrease inflammation, fight free-radicals and reactive O2, and help maintain healthy metabolic function.
Concluding that practicing some level of carb restriction is good for your long term health is hardly controversial. The trick is finding the sustainable level of restriction that works best for you. As with so many effects in health, there is a j-curve distribution of the benefits of carb restriction. This means that too much and too little are both not the optimal points for healthspan.
Somewhere in between is the right midpoint for each of us. We think there is good evidence that going to the extreme of low-carb diets once in a while is good to increase your metabolic flexibility. But doing this indefinitely may tax our system in different ways and it is certainly not fun. You should aim to keep yourself in a sustainable range where you prioritize carbs from vegetables and fruits and avoid all processed carbs. Learn to listen to your body as you dial your carbs up and down to figure out the level that works best for you.
Go deeper: learn how to refine your diet and eating habits with a continuous glucose monitor.
Have you tried carbohydrate restriction? Is it sustainable? Share your experiences with us at firstname.lastname@example.org
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