Are Low-Carb Diets a Healthy Choice?

Last Updated on August 26, 2022 by Michael Joseph

Low-carb diets are one of the most polarizing nutritional topics.

It is possible to find just as much online information praising them as it is to find information condemning them.

This article will attempt to separate the facts from the myths and answer the question: ‘are low-carb diets a healthy choice?’

What Are Low-Carb Diets?

Various Foods Suited For a Low-Carb Diet (Avocado, Eggs, Fish, Meat, Nuts, Green Vegetables).

A low-carbohydrate diet, commonly known as ‘low-carb,’ is a way of eating that limits daily carbohydrate intake.

Although certain foods are often given preference in these diets, the absolute daily carbohydrate intake defines whether or not a diet is low-carb.

Very-low-carb diets, such as the ketogenic diet, are generally defined as having a carbohydrate intake equivalent to <10% of daily calorie intake. For someone on a 2000-calorie diet, this upper limit would be approximately 50 grams of carbohydrates.

However, while the two diets are similar in some ways, general low-carb and ketogenic diets are quite different.

There is no consistent accepted definition of what upper carbohydrate intake level defines a more moderate low-carb diet.

On this note, some studies have defined low-carb as a carbohydrate level of 20% of daily calorie intake, while others have defined <45% energy from carbohydrates as low-carb (1, 2).

Additionally, some claim that anything under the carbohydrate level recommended by dietary guidelines is ‘low-carb.’

For reference, the United States National Academy of Sciences has set an acceptable macronutrient distribution range (AMDR) for all age groups. For carbohydrate intake, this AMDR is 45-65% of daily calories from carbohydrates (3, 4).

Low-carb diets can work well for several reasons, such as an emphasis on satiating foods, “rules” that work for the individual, and the removal of a wide range of calorie-dense foods.

Nevertheless, they are not magic and don’t work for everyone. Low-carbohydrate diets can be beneficial if they are the right fit for the individual.

Key Point: Low-carbohydrate diets are a dietary pattern defined by lower than recommended carbohydrate intake. Strict very-low-carb diets may only allow fewer than 50 grams of carbohydrates per day, whereas more moderate low-carb diets can vary.

What Foods Can You Eat On a Low-Carb Diet?

The simple answer is that you can eat any food on a low-carb diet, providing overall carbohydrate intake stays within the daily limit.

That said, low-carb diets tend to include more of the following foods:

  • Cheese
  • Eggs
  • Fats and oils
  • Fish
  • Fruit
  • Meat
  • Nuts
  • Seeds
  • Shellfish
  • Tofu
  • Vegetables

Mostly, these are foods with a relatively small proportion of carbohydrates compared to their fat/protein content.

Most meals will revolve around a source of protein alongside foods such as vegetables or berries, alongside an added fat source.

A lot of cutting carbohydrate intake comes from removing added sugars from the diet and limiting cakes, cookies, pastries, etc.

What Foods Can’t You Eat On a Low-Carb Diet?

Generally speaking, there are no foods that cannot fit into a low-carb dietary pattern.

However, there are certain foods that the nature of the diet limits.

For example, foods like legumes and grains can also fit into a low-carb diet providing daily carbohydrate intake stays within the individual’s target range.

Since these foods have a significantly higher carbohydrate content, there is less room for them in a true low-carb diet.

Most people consuming a low-carb diet will avoid consuming large amounts of flour or sugar-containing foods from sources such as bread, cakes, cookies, and pastries.

There are also popular low-carb bread, pasta, snack, and fast food ‘alternatives’ to conventional higher-carbohydrate options.

For people who enjoy baking, a wide range of low-carb flours can replace regular flour.

Key Point: A low-carb diet restricts total carbohydrate intake rather than specific foods. However, the diet emphasizes foods that contain a small proportion of carbohydrates.

Potential Benefits of Low-Carb Diets

All dietary interventions can have numerous potential beneficial effects, and they can also have detrimental impacts too.

This generally depends on the individual, their health circumstances, and how well (or not) the diet is formulated. For this reason, each individual should discuss any significant dietary change with their doctor or medical team.

However, scientific research into low-carbohydrate diets has consistently identified several potential benefits.

The following sub-headings provide a summary of these potential benefits.

May Help To Improve Blood Sugar Control

Low-carb diets are clinically proven to help control blood sugar levels.

Here are some of the research findings within this area from systematic reviews:

Study 1

A 2021 systematic review and meta-analysis examined twenty-three randomized clinical trials evaluating the effect of low-carb diets (<130 grams/day) in adults with type 2 diabetes (5).

In summary, in patients who adhered to the diet, low-carb diets were associated with a 32% increased remission of diabetes compared to control diets after 6 months.

Yet, these benefits faded at the 12-month mark, possibly due to lower dietary adherence – though the researchers could not confirm this.

Study 2

A meta-analysis of randomized controlled trials published in 2020 assessed the relationship between low-carb diets and glycemic control (6).

Based on thirty-seven trials involving 3301 participants, low-carb diets (average intake: 36% of total energy) were associated with short-term reductions in average blood sugar at the three-month mark.

However, there was no difference at 6 months and 12 months compared to the control diet.

For very low-carb diets, significant decreases in average blood sugar were seen at 3 months and 6 months, but not at 12 or 24 months.

Study 3

A systematic review and meta-analysis of randomized controlled trials was published in the ‘Diabetes Research and Clinical Practice’ journal in 2017 (7).

The review assessed the effect of low-carb diets (5-20% of total energy) compared to normal or high-carbohydrate diets for managing type 2 diabetes management.

Based on 9 studies involving 734 participants, low-carb diets significantly affected average blood sugar levels compared to control (weighted mean difference: 44% reduction).

Study 4

A 2018 systematic review published in the American Journal of Clinical Nutrition examined the effects of low-carb diets on metabolic control compared to low-fat diets (8).

After analyzing 33 randomized controlled trials and 3 controlled clinical trials, there was low-certainty evidence that low-carb dietary patterns lowered average blood glucose levels more than low-fat patterns in the short term.

This finding was still visible at the one-year mark but disappeared after two years.

Key Point: As the research findings show, low-carb diets appear to have an advantage over low-fat diets for blood-glucose control in the short term. However, this effect appears to fade in the longer term. Further research to confirm whether this is due to failing dietary adherence or other factors needs establishing.

May Help With Weight Loss

Alongside their clinical use for managing blood glucose in type 2 diabetes patients, low-carb diets have also demonstrated their potential as a weight loss tool.

On this note, a 2018 systematic review of existing systematic reviews looked at low-carbohydrate diets for overweight and obesity (9).

Incorporating data from 12 existing systematic reviews, low-quality data from meta-analyses suggested that low-carb diets result in increased weight loss compared to (low-fat) control.

However, the higher quality meta-analyses included in the review demonstrated “little or no difference” between diets.

Furthermore, a 2020 systematic review looked at the impact of very low carbohydrate diets on weight loss (10).

This particular systematic review found that very low-carb, high-fat (VLCHF) and low-fat (LF) dietary interventions resulted in similar weight loss levels after three months.

However, the authors of the study added an important point in their conclusion:

“VLCHF and LF diets with moderate energy restriction demonstrate similar weight loss and improvements to blood pressure to 3 months. However, adherence is likely poor without intensive support from health professionals.”

Lynda J. Ross et al (2010)

The latter part of the above statement is key; a successful diet for weight loss is one that people can sustain. For this to be the case, intensive support systems can be important, and so can personal enjoyment of the diet.

In other words, low-carb diets can potentially be a good weight loss intervention diet if they fit with the individual’s lifestyle, likes, and preferences. In addition, meeting such criteria will generally allow for greater adherence to the diet.

However, low-carbohydrate diets are not only for weight loss. As with any diet, it is possible to gain, maintain, or lose weight, depending on overall energy intake.

Key Point: If people can adhere to a well-formulated low-carb diet, it may potentially help with weight loss.

Very Low-Carb Diets Have Been Used To Successfully Treat Epilepsy

Very low carbohydrate (ketogenic) diets have been a treatment option for epilepsy since the 1920s (11).

For more information, see this guide to the ketogenic diet.

Low-Carb Diets Limit Many Energy-Dense Processed Foods

Due to its restriction on carbohydrate intake, people following low-carb diets generally limit many ultra-processed foods.

Many popular processed food options are high in carbohydrates and fat and thus very energy-dense.

To illustrate such foods, here are some examples:

  • Biscuits/cookies
  • Burgers
  • Cakes
  • Donuts
  • French fries
  • Milk chocolate
  • Pastries and pies
  • Pizza
  • Potato chips
  • Tacos and burritos

Since these are also foods that people tend to over-consume, limiting their intake could benefit some people.

Key Point: Low-carb diets tend to restrict nutritionally poor processed food options.

Low-Carb Diets Are Not Overly Restrictive

Several popular diets, such as carnivore and vegan diets, can be quite restrictive.

However, a moderately low-carb diet with about 25-35% of energy from carbohydrates can include practically any food.

If someone wishes to include dairy and meat on a low-carb diet, they can.

A low-carb diet could also be primarily plant-based in its composition and include foods such as legumes and tofu.

Higher-carbohydrate foods can also fit into the diet occasionally, providing that the diet stays within total carbohydrate intake targets.

Key Point: Moderate low-carb diets are not restrictive and can include practically all foods.

Potential Downsides of Low-Carb Diets

There are also some potential downsides of low-carb diets, as summarized in the following sub-headings.

Adherence Can Be Difficult

The simple fact is that most diets fail.

It can be very difficult for the average person to sustain any particular dietary pattern.

A meta-analysis of 29 weight loss studies with long-term follow-up found that, on average, individuals regained approximately 80% of the weight they lost over the five years following the study (12).

Specific to low-carb diets, studies have shown the following adherence rates:

  • In a 12-month clinical trial, 75 participants followed a low-carbohydrate diet (<40 grams of carbohydrate per day). Among the participants, 73.9% were within the carbohydrate intake goal after 3 months, but this fell to only 44.8% of people at 12 months (13).
  • A randomized controlled trial compared low-carbohydrate, low-fat, and Mediterranean dietary patterns for weight loss. At the 24-month mark, adherence in the low-carbohydrate diet group was 78% (14).

Also, it is important to note that these adherence rates were in research studies where participants received strong support and information from knowledgeable scientists.

In the real world, it can be even harder to adhere to a diet, particularly if that diet isn’t the right fit for the individual.

Research has suggested factors such as nutrition knowledge, socioeconomic means, the inclusion of culturally appropriate foods, and strong support systems can all influence adherence to diets (15, 16, 17).

For a low-carb diet to be successful, it must be the right fit for the individual.

Key Point: As with all diets, it can be difficult to adhere to a low-carbohydrate diet. For greater adherence, the diet must fit the individual and their lifestyle.

May Increase LDL-Cholesterol (LDL-C) Levels

Low-carbohydrate diets can have important clinical benefits, such as weight loss and lowering triglyceride levels (18).

However, they can sometimes also increase LDL-C levels, particularly if the diet is high in saturated fat and low in polyunsaturated fatty acids (19, 20).

There are many risk factors for cardiovascular disease, including genetic risk, older age, weight, low physical activity levels, smoking, blood lipids, blood pressure, diabetes, and more (21, 22).

That said, higher LDL-C levels are significantly associated with increased cardiovascular risk, all else equal (23).

It is important to note that low-carb diets do not have to raise LDL-C levels. For instance, a low-carb diet that met the following criteria would likely decrease LDL-C:

  • Limiting saturated fat intake to 10% of total calorie intake (24, 25)
  • Consuming lower-carb, high-fiber foods such as fruit, vegetables, legumes, and psyllium (26, 27, 28)
  • Consuming sources of polyunsaturated fat such as nuts and seeds (29, 30)

Anyone concerned about their blood lipid profile should speak with their doctor or medical team.

Key Point: Depending on the formulation of the diet, low-carb diets may potentially raise LDL-C levels. Higher LDL-C levels are associated with increased cardiovascular risk.

Low-Carb Diets Are Probably Not Optimal For High-Intensity Exercise

It is a myth that carbohydrates are necessary to fuel exercise.

However, just because carbohydrates aren’t required for exercise, it does not automatically follow that restricting their intake is optimal.

On this note, several systematic reviews have assessed the effects of low-carb diets on strength and performance compared to higher carbohydrate diets.

Review 1

A recent 2022 systematic review on the effect of carbohydrate intake on strength and resistance training performance looked into the existing research (31).

This review found no significant differences between high- and low-carbohydrate diets for strength training performance.

However, the review suggested that longer workouts with more than 10 sets per muscle group may benefit from a higher carbohydrate intake.

Review 2

Another 2022 systematic review and meta-analysis examined the effects of a very low-carb (ketogenic) diet on performance in athletes and trained adults (32).

This review included 18 studies that involved cyclic exercise, strength (one repetition max weight), and body composition.

Overall, a high-carbohydrate-rich diet had an advantage over the very low-carb diet for time-trial results and lean body mass. Additionally, the low-carb diet did not have a favorable impact on increasing strength, as measured by one rep max.

However, the results favored the low-carb diet for total weight and fat mass losses.

Review 3

A 2021 systematic review examined the impact of high-fat ketogenic diets on physical performance (33).

This review compared the effect of consuming <50 grams of carbohydrates per day to a more conventional diet that had a fat content ranging from 12-38% of total calories.

Based on 13 endurance outcomes and 16 strength and power outcomes, the review demonstrated that:

  • Endurance performance was lower on the ketogenic diet in three outcomes, whereas there were no significant differences compared to control in ten outcomes.
  • Strength and power performance was lower on the ketogenic diet in three outcomes, there were no significant differences in eleven outcomes, and performance was higher in two outcomes.

Overall, it can be argued that the results slightly leaned toward the high-carbohydrate diet for endurance. However, for the most part, there were no significant differences between the low-carb and high-carb performance results in this systematic review.

The authors of this systematic review noted that “Future investigations should consider assessing time-course changes in physical performance, and powering sample sizes to examine the effects of training status and/or sex on physical performance following a ketogenic diet compared with conventional.”

In other words, more tightly controlled research is necessary to understand why outcomes differ in some studies, and larger, more rigorous studies should help to ascertain this.

Key Point: The existing scientific literature appears to favor high-carbohydrate diets for exercise performance. However, research is ongoing in the area.

May Raise the Risk of Vitamin and Mineral Insufficiency

Restricting a large range of foods from the diet, as low-carbohydrate diets do, can potentially raise the risk of insufficient intake of various vitamins and minerals.

This is true of any diet that emphasizes restrictions, whether vegan, low-carb, or any other.

Notably, a systematic review published in 2019 investigated the impacts of carbohydrate-restricted diets on micronutrient intake and status (34).

This systematic review identified 10 studies, including 7 randomized controlled trials, where a lower-carbohydrate diet (ranging from 4% to 34% of calories) was prescribed.

In summary, there was a significantly decreased intake of thiamin, folate, magnesium, calcium, iron, and iodine (from -10% to -70% of baseline intake) with any carbohydrate-restricted diet trial.

Despite this, it is important to note that a well-formulated low-carbohydrate diet can meet all vitamin and mineral requirements.

For more information, see this guide on how to get a sufficient intake of every vitamin and mineral on a low-carb diet.

Key Point: Low-carbohydrate diets can potentially decrease the intake of several essential vitamins and minerals. However, well-formulated low-carb diets can provide adequate vitamin and mineral intakes.

What Might Low-Carb Meals Look Like?

Here are some varied and simple meal ideas to better understand how low-carb meals might look.

Breakfast

  • Yogurt, mixed nuts, and berries
  • Scrambled eggs, smoked salmon, and an assortment of vegetables
  • Shakshuka: a Middle-Eastern dish involving poached eggs cooked in a spicy tomato sauce
  • Cheese and onion omelet
  • Kippers or sardines with sauteed leafy greens
  • Bacon, egg, grilled mushrooms, and tomato

Lunch

  • Pieces of chicken in a leafy green salad with cherry tomatoes, red onions, balsamic vinegar, and olive oil
  • Greek yogurt mixed with pieces of dark chocolate, blueberries, and mixed nuts
  • Three hard-boiled eggs, a cup of fresh berries, and an avocado
  • A glass of whole milk, a handful of almonds, and an apple
  • Ricotta cheese, sliced tomato, walnuts, black olives, and leafy greens drizzled with olive oil, lemon juice, and balsamic vinegar
  • A piece of cheese, a handful of nuts, some berries, and an avocado

Dinner

  • Fillet of salmon served alongside sauteed carrots, chives, leeks, and onions
  • Baked mackerel, steamed leafy greens, a sweet potato, and dark chocolate for dessert
  • Beef steak with mushrooms and an assortment of sauteed vegetables
  • Baked tofu marinated with soy sauce, served with roasted garlic, onions, and broccoli
  • Chicken breast or thigh smothered in a melted Cheddar and chive sauce served with green beans and mushrooms
  • Grilled shrimp served with roasted asparagus, carrots, and onions

As shown in these examples, lower-carbohydrate meals can be quite varied.

For more ideas, there are some low-carb recipe ideas here and here.

Key Point: Low-carb meals can incorporate a wide range of different foods.

Common Questions About Low-Carb Diets

There are many common questions about low-carb diets.

Here is a rundown of some of the most typical.

Are Low-Carb Diets Low In Fiber?

A low-carbohydrate diet may be low in fiber or very fiber-rich, depending on the diet composition.

Low-carb diets limit several fiber-rich food sources, such as whole grains and legumes.

However, there are also many low-carb-friendly fiber sources, such as avocados, berries, and leafy green vegetables.

For further information, here are some of the best low-carb, high-fiber foods.

Are Low-Carb Diets High In Saturated Fat?

Once again, whether a low-carb diet is high in saturated fat or not depends on the formulation of the diet.

Some cooking fat options, such as beef tallow and butter, are very high in saturated fat.

However, other cooking oils like olive oil and Canola have a minimal saturated fat content.

Whole food fat sources can also be high or low in saturated fat, depending on the specific food.

Which Fruit and Vegetables Can You Eat On a Low-Carb Diet?

As previously mentioned, eating any food on a low-carb diet is possible if it fits within the total daily carbohydrate target.

Regardless, some fruits and vegetables are more conducive than others for this purpose.

For this reason, leafy greens like spinach tend to feature in low-carb diets more than potatoes do.

Regarding fruit, blackberries and raspberries contain significantly fewer carbohydrates than mangos and pineapples.

For further examples, here are some of the lowest-carb fruits and lowest-carb vegetables.

What Are the Best Drinks For a Low-Carb Diet?

Water is the optimal drink for humans, whether they are on a low-carb diet or not (35).

Other drinks that can fit well with a low-carbohydrate diet include black tea, coffee, green tea, herbal tea, diet soda, and milk (in moderation).

For a guide to almost every common drink alongside their full cab counts, see this low-carb drinks guide.

Can You Consume Alcohol On a Low-Carb Diet?

It is possible to include alcohol on a low-carb diet if one wishes to do so and understands the potential risks of alcohol.

However, many types of alcohol contain large amounts of carbohydrates and aren’t particularly suited for a “low-carb” diet. In other words, some choices are better than others.

Numerous low-carb beers and low-carb wine options also cater to people following low-carbohydrate diets.

Are Low-Carb Diets a Healthy Choice?

Overall, whether a low-carb diet is a healthy choice will depend on several factors:

  • Is it the right choice for the individual? Does the diet fit with the individual’s lifestyle and food preferences? Can they enjoy and sustain the diet?
  • Is the diet well-formulated? Low-carb diets can come in all shapes and sizes. However, nutritionally, there is a significant difference between living off hot dogs, bacon, and butter compared to a broader diet that includes a varied food intake from dairy, fruit, meat, nuts and seeds, seafood, and vegetables.

If a low-carb diet is formulated well and fits the lifestyle of the person following it, then it can be a healthy and sustainable choice.

That said, discussing any new diet with a doctor before starting it is always a good idea, particularly if a medical condition is involved.

For more information on different diets, see this review of popular diets.

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Todd
Todd
30 days ago

Every nutritionist seems to tip toe around the biggest issue. That being that processed foods in the standard American diet have severe health consequences. To call out carb restriction as anything other than healthful misses the point.