Are low-carb meals sufficiently nutritious?

• Due to their restrictive nature, low-carbohydrate diets, which provide less than 130 grams of carbohydrates per day, are often viewed as nutrient-deficient diets.
• However, a recent study analyzed the calorie and nutrient levels provided by well-planned low- and very-low-carbohydrate diet plans, suggesting they can meet some of the nutrient needs of certain populations, particularly middle-aged women.
• While these diet plans can offer some benefits, they don’t seem to meet the nutrient needs of all individuals equally, as they may lack some key nutrients while exceeding recommendations for others.
• More research is needed, but health professionals recommend sticking with moderate to high consumption of carbohydrates from nutrient-dense, plant-based foods for optimal health.

Low-carbohydrate diets are increasingly popular despite ongoing debates about the diet’s nutritional value and long-term health effects.

Now, adding to the discussion, a new study published in Frontiers in Nutrition assessed the calorie and nutrient content of three well-planned 7-day low-carb diet plans.

However, none of the low-carbohydrate meal plans could meet all of the calorie and nutrient needs of each studied gender and age group.

The study received funding from Simply Good Foods USA, Inc, which owns Atkins and Quest Nutrition, brands selling low-carbohydrate food products.

Additionally, two of the three study authors are declared employees, and one is a Simply Good Foods USA, Inc. shareholder.

Medical News Today contacted Simply Good Foods for comment regarding the study’s funding and reported conflicts of interest.

In response, Jonathan Clinthorne, PhD, study author and the Senior Director of Nutrition at Simply Good Foods, told MNT that: “The funder designed and analyzed the dietary pattern modeling using publicly available datasets and helped write the manuscript, alongside a third-party expert. The study underwent peer-review to ensure scientific integrity of the work.”

Clinthorne further stated:

“The goal of this study was to determine whether different levels of carbohydrate restriction could provide adequate nutrition, as this is a common question regarding lower carbohydrate diets. The study uses food pattern modelling, which is an easily repeatable process for the research community, it went through peer-review to ensure scientific integrity of the work, and we followed the COI disclosure practices required by the journal. The study also transparently demonstrates both the nutrients of adequacy and of concern when following these types of dietary patterns, which can help advance the scientific dialogue around low-carbohydrate diets.”

Typically, low-carb diets involve consuming less than 130 grams (g) of carbohydrates daily, accounting for less than 26% of a person’s daily calorie intake.

Very low-carbohydrate diets are even more restrictive, with only 20–50 g of carbohydrates per day, representing less than 10% of daily calories.

The researchers developed three specific diet plans, each providing 20, 40, or 100 g of net carbohydrates and varied amounts of other nutrients and calories daily.

“Net carbohydrates” refer to those digestible by humans, calculated by subtracting fiber and sugar alcohols from the total carbohydrates on a food label.

The food items were intentionally chosen to address nutrients of public health concern identified in the 2020–2025 Dietary Guidelines for Americans and to fit within guidance generally found in clinical studies of low carbohydrate diets and from professional societies.

The researchers assessed how well these plans met the recommended dietary allowances for men and women ages 31–50 and 51–70.

For women, the three 7-day low-carbohydrate meal plans generally met or exceeded daily calorie needs, but only the 100-gram carbohydrate plan fully covered calorie requirements for middle-aged women while surpassing them for older women.

On the other hand, for men across both age groups, all of the meal plans failed to meet recommended daily calorie intakes.

The meal plans, which replace carbohydrates with fats, naturally contained higher fat and lower carbohydrate levels than generally recommended. Protein intake in these meal plans was above the recommended daily allowance for both genders but fell within the acceptable macronutrient range.

Both men and women of each age group on these plans would receive more than enough of several vitamins, including A, C, D, E, K, thiamin, riboflavin, niacin, B6, folate, and B12, without exceeding safe upper limits.

The plans also provided ample calcium for adults aged 31–50 but failed to meet the calcium needs of older adults.

Iron intake in these meal plans was adequate for males and older females, but middle-aged women — who require more iron — would not get adequate iron, except on the 100-gram carbohydrate plan.

Saturated fat made up a significant portion of the total calories in each plan, with 21% in the 20-gram diet, 19% in the 40-gram diet, and 13% in the 100-gram diet. However, these plans had a better omega-6 to omega-3 fatty acid ratio than the average American diet, potentially providing protective health effects.

Fiber intake, often a concern with low-carbohydrate diets, showed varied results. Middle-aged males would not meet minimum fiber recommendations on these meal plans, while females would exceed them on the 40- and 100-gram carbohydrate diets. Older females and males on the higher carbohydrate plans would also meet fiber requirements.

Adequate fiber intake is necessary to support a healthy intestinal system and control cholesterol levels.

The 100-gram carbohydrate meal plan, being the least restrictive, came closest to meeting nutrient goals, particularly for middle-aged women. However, even as a well-planned diet, it still falls short in some key nutrients while exceeding recommended limits in others.

MNT spoke with Thomas M. Holland, MD, MS, a physician-scientist and assistant professor at the RUSH Institute for Healthy Aging, RUSH University, College of Health Sciences, who was not involved in the study, to discuss the potential effects of the outlined 100-gram carbohydrate meal plan.

The 7-day low carbohydrate meal plan included animal products at nearly every meal, such as eggs, dairy products, meat, poultry, or fatty fish like salmon, mackerel, sardines, or tuna.

Holland noted that the benefits of a similar meal plan “may come primarily from the inclusion of high-quality protein sources like dark, fatty fish,” which provides heart-healthy omega-3s linked to lower cognitive decline and reduced heart disease risks.

The regular inclusion of fatty fish likely led to the preferable omega-6 to omega-3 ratio in the meal plans.

However, the saturated fats from the full-fat dairy and red meats, which exceeded recommended limits, could increase LDL (bad) cholesterol and cardiovascular disease risks.

“Therefore,” Holland said, “while animal proteins offer benefits, the type of animal protein and overall dietary composition matter significantly.”

Overall, when considering a diet for optimal health, Holland stated:

“While an animal-heavy low-carb diet may provide certain benefits, especially when it includes healthy protein sources like fish, a plant-based diet that emphasizes high-quality, whole foods isgenerally superior for cardiovascular health, particularly due to its higher fiber and phytochemical content.”

The study authors acknowledge that this analysis has limitations, such as not utilizing data from real dietary intake among free-living individuals to develop meal plans based on more commonly consumed foods, and not factoring in dietary supplements.

They caution that like any meal planning for specific population groups, the meal plans and study findings should not be personalized without accounting for age, gender, physical activity, and preexisting conditions.

Alyssa Simpson, RDN, CGN, CLT, a registered dietitian, certified gastrointestinal nutritionist, and owner of Nutrition Resolution in Phoenix, AZ, who was not involved in the study, told MNT that while the study shows that low-carb diets might be nutritionally adequate for certain groups when carefully planned, “the challenge lies in whether people are building high-quality, well-balanced diets in real life.”

“Many low-carb diets rely on ultra-processed products, which may not offer the same health benefits as whole, nutrient-dense foods,” she emphasized.

She noted that, for example, ultra-processed foods like “low-net-carb bars and shakes can be convenient for those following a low-carb diet, but it’s essential to choose products with high-quality ingredients and minimal artificial sweeteners.”

Simpson said that “ensuring that low-carb diets are both nutritionally complete and made up of high-quality, minimally processed foods is critical for achieving the best health outcomes.”

Ultimately, regarding this study’s low-carbohydrate diet patterns, she concluded:

“While low-carb diets can offer benefits, their long-term sustainability and adherence can be challenging. The study’s meal plans, though nutritionally adequate, may not fully address the practical difficulties individuals face in maintaining such diets over extended periods.”