Quick Answer
Tomatoes can be eaten in moderation on a low carb diet. One medium tomato has around 5 grams of net carbs, so they can fit into a low carb eating plan as long as portions are controlled. Many low carb diets allow 20-50 grams of net carbs per day, so one tomato would account for 10-25% of the daily carb allowance on stricter low carb diets. Tomatoes are a healthy food rich in nutrients like vitamin C, vitamin K, potassium, folate and lycopene. People following a low carb diet may still benefit from eating tomatoes in moderation.
How Many Carbs Are in Tomatoes?
The total carb content of tomatoes is around 4-5 grams per 100 grams or 3.5-4 grams in an average medium sized tomato (123g) [1].
However, the net carb content is lower when you account for the fiber in tomatoes. The fiber is indigestible by humans and doesn’t impact blood sugar levels like other carbs.
An average medium tomato with 123g weight contains around 5g of total carbs and 1.5g of fiber. So the net carb count comes out to around 3.5g of net carbs per average medium tomato.
Here is a breakdown of the carb content in 100g and a medium tomato:[2]
| Tomatoes (100g) | Medium Tomato (123g) |
|---|---|
| Total carbs: 4g | Total carbs: 5g |
| Fiber: 1g | Fiber: 1.5g |
| Net carbs: 3g | Net carbs: 3.5g |
So a medium tomato of average size has about 3.5 grams of net digestible carbs.
Daily Net Carb Allowance on Low Carb Diets
The amount of net carbs allowed per day can vary significantly depending on the type of low carb diet.
Here are some typical net carb allowances on popular low carb diet protocols:
– Standard Ketogenic Diet (SKD): 20-50 grams per day[3]
– Targeted Ketogenic Diet (TKD): Around 50 grams per day
– High Protein Ketogenic Diet: 60-120 grams per day
– Atkins Diet: Starts at 20g net carbs and slowly increases to 50-100g per day as you approach goal weight[4]
– Paleo Diet: Typically 100-150g per day or less than 45% of calories from carbs[5]
So on a standard ketogenic diet or in the induction phase of Atkins 20-50g net carbs is typical. A single medium tomato with 3.5g net carbs would account for about 7-18% of the daily carb intake target on these stricter low carb diets.
On more moderate low carb diets like Paleo or higher protein ketogenic diets, a tomato would be less than 5% of the typical 100-150g daily net carb goal.
So tomatoes end up being a larger percentage of the daily allowance on very low carb keto diets under 50g net carbs, versus more moderate low carb diets up to 150g net carbs.
This means tomatoes and other carb containing veggies and fruits often need to be limited on stricter keto, but can be more liberally incorporated into versions of low carb with higher carb allowances.
Nutrition Benefits of Tomatoes on Low Carb Diets
Despite being a vegetable fruit that contains carbs and sugar, tomatoes are very nutritious.
Some of the many nutrients found in tomatoes include[6]:
– Vitamin C: 28% DV in a medium tomato
– Vitamin K: 12% DV
– Potassium: 12% DV
– Folate: 12% DV
– Vitamin E: 5% DV
– Vitamin B6: 5% DV
– Magnesium: 4% DV
– Phosphorus: 4% DV
– Copper: 4% DV
Tomatoes are also an excellent source of lycopene, a red carotenoid pigment that gives tomatoes their red color. Lycopene has been linked to many health benefits including:[7]
– Reduced risk of heart disease
– Potential protective effects against cancer
– Improved skin health
– Lower oxidative stress and inflammation
Even on very low carb diets tomatoes can contribute to achieving greater vitamin, mineral and antioxidant intake in limited amounts. This makes them a healthy plant to consume in moderation on most low carb eating approaches.
Tips to Fit Tomatoes Into a Low Carb Diet
Here are some tips for fitting tomatoes into your diet if you are restricting overall carb intake:
– Measure portion sizes using a food scale or measuring cups to stick to around 1 medium tomato (123g) or less per meal. This will provide about 3.5g net carbs.
– Time your tomato intake around workouts on TKD/Targeted Keto diets to take advantage of the carb content for energy.
– Focus on eating tomatoes raw instead of cooking down into sauces or juices which can concentrate the carbs and sugars.
– Substitute recipes calling for high carb ingredients like sugar or grains with tomatoes to increase nutrients.
– Pair tomatoes with healthy fats like olive oil and cheeses or protein sources to slow digestion.
– Use cherry or grape tomatoes instead of large tomatoes to portion control carb intake at meals.
As long as you focus on controlling portion sizes, tomatoes can be included even in strict low carb diets of 50 grams of net carbs or less. Their vitamin, mineral and antioxidant contents make tomatoes a healthy plant food to eat in moderation on low carb.
Potential Issues With Tomatoes on Low Carb
While tomatoes are usually viewed as safe and healthy for low carb diets, there are a few potential issues to keep in mind:
Blood Sugar Spikes
Since tomatoes do contain around 3.5 grams of net digestible carbs, they can potentially spike blood sugar levels right after eating for those with diabetes or metabolic conditions.
Controlling portions and combining with fats, protein and fiber can slow the carb absorption and reduce this effect.
Nightshade Sensitivity
Tomatoes belong to the nightshade group of vegetables like peppers, eggplants and white potatoes. Some people have sensitivities to nightshades and may experience digestive issues or worsening of autoimmune diseases after eating them [8].
Removing nightshades including tomatoes from your diet can help determine if they are problematic for you. Reintroducing them one at a time can pinpoint the potential trigger foods.
Histamine Issues
Tomatoes can also sometimes trigger histamine issues in susceptible individuals. Histamine intolerance can lead to symptoms like:[9]
– Rashes or skin irritation
– Runny nose and congestion
– Headaches
– Fatigue
If you experience these types of reactions after eating tomatoes, it may be a sign of a histamine intolerance that may require avoiding tomatoes.
Gut Irritation
For those with irritable bowel syndrome (IBS) or other gut conditions, the seeds in tomatoes may potentially irritate the digestive tract. This is due to their small size which resists digestion.
Removing the seeds may reduce this irritation. Tomato sauces can also be easier to digest for those with gut issues compared to raw tomatoes.
As with any food, it’s important to monitor your individual response to figure out if tomatoes need to be avoided or limited in your diet. While healthy for most, they can potentially cause issues in sensitive individuals.
Better Low Carb Substitutes for Tomatoes
If you find that tomatoes need to be very restricted or avoided in your diet, here are some lower carb vegetables you can substitute in recipes:
– Leafy Greens – Spinach, kale, lettuce and other leafy greens can be used in place of sliced tomatoes on sandwiches, burgers and wraps. They provide fiber, vitamins and minerals without the carbs in tomatoes.
– Cucumbers – Sliced cucumbers can replicate the juicy crunch of tomatoes on low carb diets. They contain just 3 grams of net carbs per cup.
– Cabbage – Red or green cabbage heads shredded or chopped can mimic the texture of chopped tomatoes at 4 grams of net carbs per cup.
– Zucchini – Spiralized or diced zucchini can substitute for tomatoes in Italian dishes, sauces and salads with just 3 grams of net carbs per cup.
– Peppers – While also nightshades, red, yellow or orange peppers have 5 grams of net carbs per cup and can replace tomatoes in salsa and salads.
– Avocado – The creamy texture of avocados can be a smooth tomato sauce substitute and packs in healthy fats with only 2 grams of net carbs per 100 grams.
– Mushrooms – Varieties like portobello can be “roasted” and chopped as a savory replacement for tomatoes with minimal carbs.
While tomatoes are often included in low carb diets for their beneficial nutrients, you have solid low carb alternatives if you need to restrict intake or replace them entirely.
Final Thoughts on Tomatoes and Low Carb Diets
Can You Eat Tomatoes on Keto?
Tomatoes can be eaten in small portions as part of keto and very low carb diets under 50g net carbs per day. About 1 medium tomato with 3.5g net carbs can fit into the daily allowance, but tomatoes should be limited to 1 serving per day at most.
Are Tomatoes Low Carb?
Tomatoes are not extremely low in carbs, containing around 3.5g net carbs in a medium sized tomato. However, they are lower in net carbs than many other fruits and starchy vegetables, allowing them to be used in small amounts on reduced carb diets.
Should You Avoid Tomatoes on Low Carb?
Most people can fit tomatoes into a low carb diet in moderation. However, some people with sensitivities may need to avoid tomatoes if they lead to issues like digestive problems, histamine reactions or worsened autoimmunity. Pay attention to how your body responds to tomatoes to determine if you should avoid them.
Can You Substitute Tomatoes in Low Carb Recipes?
If a low carb recipe calls for a large amount of tomatoes that don’t fit your macros, you can often replace them with lower carb options like leafy greens, cucumbers, zucchini, mushrooms, peppers or cabbage. This allows you to reduce the carbs while still getting beneficial nutrients.
Conclusions
Tomatoes contain enough net carbohydrates that they need to be portion-controlled on lower carb diets. But they can be eaten in moderation as part of healthy low carb and keto diet plans. One medium tomato provides about 5g total carbs and 3.5g net carbs. This fits into a typical low carb intake between 20-50g daily. Tomatoes provide beneficial nutrients like vitamins, minerals and antioxidants. But be cautious with tomatoes if you have sensitivities, gut issues or health conditions aggravated by nightshades. Overall tomatoes can be part of a healthy low carb diet when controlled portions are emphasized.