Published 5th October 2022

Should you consider a low-carb diet?

Having a low-carb diet involves limiting your intake of carbohydrates. 

Historically, many people saw low-carb diets as a way to lose weight. But there’s been growing interest in using them to help manage prediabetes, type 2 diabetes, and other metabolic health conditions. 

There are also anecdotal reports of improved energy levels, better cognition, and improved mood among people with low- or very low-carb diets. Still, there isn’t evidence from any large studies yet. 

Current guidelines recommend that you get 45–65% of your daily energy intake from carbs. For someone eating about 2,000 calories a day, this would mean consuming about 220–325 grams of carbs every day. 

There’s no standard definition of “low” carbs. 

Most researchers calculate it as a percentage of overall intake — as getting less than 26% of your daily calories from carbs. This means under 130 g a day for someone consuming 2,000 calories a day.

Here are some potential benefits and risks of switching to a low-carb diet.

What is a low-carb diet?

The idea that lower insulin levels will improve your metabolism and lead to weight loss is the scientific basis of this type of diet.

After you eat, your body breaks down carbs into simple sugar molecules called glucose.

As levels of glucose in your blood rise, your pancreas secretes insulin. This is a hormone that prompts your cells to take up glucose for energy or storage. 

When carb intake is severely low — under 20 g a day —  for a number of days and your body has no more stored glucose, your insulin levels drop.

At this point, your body starts to use fat as a main source of energy. This causes your liver to make chemicals called ketones, and your body can use these as a fuel.

There are different types of low-carb diet. But it tends to mean that carbs make up around 10–25% of your daily energy intake.

You might eat 50–130 g of carbs every day, and these may come from legumes, vegetables, fruits, and whole grains. 

A very low-carb, or ketogenic, diet means that 5–10% of your daily energy intake, or 25–50 g, comes from carbs. And you typically wouldn’t eat most of the carb-containing foods in a low-carb diet. 

Instead, a keto diet is very high in fat, which would make up around 70–80% of your daily energy intake, with the rest coming from protein. This might mean eating or 150–180 g of fat a day.

Possible benefits

According to supporters, low-carb diets have a variety of health benefits. But is there quality evidence to back this up? Let’s dive into what the science says.

Weight loss

Evidence suggests that carb-restricted diets may help some people lose weight in the short term. Though at first, this is typically water weight, fat loss can occur over time.

In one meta-analysis of 38 studies, the researchers found that a low-carb diet (with under 40% carbs) may be associated with slightly more weight loss than a low-fat diet over 1 year.

The overall agreement is: Diets that restrict energy intake for under 6 months and are either low- or very low-carb may be better for weight loss, compared with diets that restrict energy intake and are low in fat.

But in the longer term, meaning 6 months or longer,  there seems to be no difference. 

Carb-restricted diets, like the keto diet, may help aid weight loss by:

  • decreasing appetite

  • managing food cravings

  • burning more calories by turning fat and protein into glucose

  • burning fat while maintaining lean body mass

Still, many people find a low-carb diet difficult to keep up. And research shows that once people go back to their regular diets, there's no lasting effect on their weight — the same as if they had been on a low-fat diet.

Weight loss maintenance 

While it's unclear if a low-carb diet can support long-term weight loss, evidence from a recent study suggests that a low-carb diet might be beneficial once you've reached a moderate weight for you.

The study included over 150 adults that had overweight or obesity. After the participants lost 12% of their body weight, the researchers randomly assigned them to one of three diets: high carb, moderate carb, or low carb.

In the first group, carbs made up 60% of a participant’s energy intake, 40% for the second group, and 20% for the third group.

After 20 weeks, the team found that the low-carb group burned an average of 209 calories more per day than those in the high-carb group. 

Overall, the researchers concluded that for every 10% reduction in carb intake, participants burned an average of 52 additional calories.

While these results are interesting, this is only one study. Fully understanding how low-carb diets affect weight management requires more research.

Managing type 2 diabetes

For many people with type 2 diabetes, controlling your carb intake is a part of everyday life.

Evidence suggests that a low-carb diet or a very low-carb diet may be linked with diabetes remission. For these diets, carbs made up under 26% or under 10% of a person's energy intake, respectively.

The researchers found that participants following a low-carb diet were 23% more likely to go into diabetes remission, compared with the control diet group after 6 months.

Interestingly, they found that the very low-carb diet group did not have the same results — maybe because of the difficulty of sticking to such a restrictive diet. 

After 6 months, the low-carb diet group also had improved weight, blood fat, and insulin sensitivity. However, these improvements were reduced at the 12-month mark. 

Overall, figuring out how a low-carb diet affects diabetes management in the long term requires more research.

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Cardiovascular health

Research into the relationship between low-carb diets and cardiovascular health is mixed.

High-quality sources of carbs provide your body with fiber. These sources include foods like grains, fruits, and vegetables.

Research has associated a high fiber intake with improved cholesterol levels and a decreased risk of heart disease. 

There’s also some evidence linking a very low-carb diet to improved heart health measures, including better cholesterol and blood fat levels, less inflammation, and lower blood pressure. 

Meanwhile, some studies have associated low-carb diets with higher levels of “bad” cholesterol. But it’s not clear whether this rise is significant. 

Scientists need to do more work to understand how low-carb diets may affect cardiovascular health.

The risks

Because it’s so restrictive, a low-carb diet can be challenging for some people to follow in the long term. Staying on track can be especially difficult at restaurants or parties, or during the holidays, for example.

And while there may be health benefits, there are also some risks to consider. 

Low-carb diets may not be safe for everyone. If you’re considering making the switch, speak with a healthcare provider first.

Vitamin deficiencies

To get all the nutrients you need, it’s important to have a healthy, varied diet full of high-quality foods. Because low-carb diets restrict your intake of many foods, you could miss out on vital nutrients.

Evidence from 10 studies showed a link between low-carb diets and similarly decreased intakes of:

  • vitamin B1

  • vitamin C

  • folate

  • magnesium

  • calcium

  • iron

  • iodine

Other studies have found that some low-carb diets only meet approximately 44% of your nutrient needs.

Changes to your gut health

There’s limited evidence about how low-carb diets affect your gut microbiome — the trillions of microorganisms living in your gut. But some studies point to a possible negative effect.

A recent review suggested that low-carb diets may change the levels of beneficial bugs in your gut. Specifically, this type of diet may lower the count of the beneficial bugs Roseburia and Eubacterium rectale.

Another study found that participants with a very low-carb diet had lower levels of another beneficial type of gut bug: Bifidobacterium.

It seems that low-carb diets may lead to changes in the microbiome, but scientists still don’t know how this may affect health in the long term. More research is needed.

Other risks

Over a long period, very low-carb diets, like the keto diet, may lead to other negative health effects, such as:

  • kidney stones

  • osteoporosis

  • elevated levels of a waste product called uric acid in the blood

Foods to focus on

If you decide to switch to a low-carb diet, try to fill your plate with a variety of healthy foods, like non-starchy vegetables, lean proteins, and healthy fats.

Foods to include: 

  • Prioritize leafy green vegetables and pulses.

  • Still eat whole fruits.

  • Opt for unsweetened milk or plant milk and yogurt. 

  • Switch to higher-fiber foods, like wholegrain bread, rice, and pasta.

  • Include more healthy fats from foods like oily fish, nuts, and seeds.

Foods to limit:

  • Try to reduce saturated fats from processed meats, biscuits, cakes, and pastries. 

  • Limit your intake of free sugars from fizzy drinks and fruit juices. 

  • Try to eat fewer highly processed, starchy foods, like white bread, rice, and flour.

Summary

Having a low-carb diet involves limiting your intake of carbohydrates. This often means that carbs contribute less than 26% of your daily calories.

There may be health benefits, like weight loss and weight management, improved heart health, and type 2 diabetes management. 

There are also risks, including nutrient deficiencies. And there’s plenty we don’t know yet, like the long-term effect on cardiovascular and gut health.

Low-carb diets can be restrictive, but they can still include a diverse range of healthy, nutrient-dense foods. These include non-starchy vegetables, fruits that are naturally low in sugar, lean meats, and healthy fats.

If you’re considering a low-carb diet, speak with a healthcare professional to see if it’s right for you.

At ZOE, we believe that eating the best foods for your body is one of the best ways to improve your overall health. Everyone’s responses to food are different, so a one-size-fits-all approach doesn’t work. 

With the ZOE at-home test, you can learn about your blood sugar and blood fat responses, and discover which “good” and “bad” bugs are living in your gut. With this information, we'll provide diet advice tailored to your unique body.

Take our free quiz to get started.

Sources

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Dietary fiber is beneficial for the prevention of cardiovascular disease: An umbrella review of meta-analysis. Journal of Chiropractic Medicine. (2017). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5731843/

Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission: Systematic review and meta-analysis of published and unpublished randomized trial data. BMJ. (2021). https://www.bmj.com/content/372/bmj.m4743

Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: An open-label, non-randomized, controlled study. Diabetes Therapy. (2018). https://pubmed.ncbi.nlm.nih.gov/29417495/

Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: a randomized trial. BMJ. (2018). https://www.bmj.com/content/372/bmj.m4743

Get smart on carbs. (n.d.). https://diabetes.org/healthy-living/recipes-nutrition/understanding-carbs

Influence of diet on the gut microbiome and implications for human health. Journal of Translational Medicine. (2017). https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-017-1175-y

Ketogenic diet. StatPearls. (2022). https://www.ncbi.nlm.nih.gov/books/NBK499830/

Ketogenic diets alter the gut microbiome resulting in decreased intestinal Th17 cells. Cell. (2020). https://www.sciencedirect.com/science/article/pii/S0092867420304906

Low and reduced carbohydrate diets: challenges and opportunities for type 2 diabetes management and prevention. Proceedings of the Nutrition Society. (2020). https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/low-and-reduced-carbohydrate-diets-challenges-and-opportunities-for-type-2-diabetes-management-and-prevention/4FCA518B172DA8AB724A2CD025984B91

Low carbohydrate diet. StatPearls. (2022). https://www.ncbi.nlm.nih.gov/books/NBK537084/

Non-starchy vegetables. (n.d.). https://diabetes.org/healthy-living/recipes-nutrition/eating-well/non-starchy-vegetables

Nutritional goals for each age/sex group used in assessing adequacy of UDSA food patterns at various calorie levels. (n.d.). https://health.gov/our-work/nutrition-physical-activity/dietary-guidelines/previous-dietary-guidelines/2015/advisory-report/appendix-e-3/appendix-e-31a4

Prevalence of micronutrient deficiency in popular diet plans. Journal of the International Society of Sports Nutrition. (2022). https://www.tandfonline.com/doi/full/10.1186/1550-2783-7-24

Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors. Journal of Clinical Lipidology. (2019). https://www.lipidjournal.com/article/S1933-2874(19)30267-3/fulltext

The effect of a low-fat and low-carbohydrate diets on weight loss and lipid levels: A systematic review and meta-analysis. Nutrients. (2020). https://www.mdpi.com/2072-6643/12/12/3774/htm

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