Keto Sardine Bone Broth Soup with Parmesan
Canned sardines, with their soft, cooked-in bones, are one of the few non-dairy sources of bioavailable calcium: approx. 380 mg per 100 g. Combined with bone broth (sodium, collagen, minerals) and baby spinach (potassium, magnesium), they create a soup that covers four electrolytes in a single meal, at just 3 g of net carbs.
Key facts at a glance
- Approx. 20 minutes to make, a complete electrolyte meal from the pantry.
- Approx. 3 g net carbs and 14 g fat per serving.
- Ingredients: canned sardines, bone broth, baby spinach, parmesan, olive oil, garlic.
- Ideal for anyone who wants to get calcium and sodium on keto through fish and broth rather than dairy.
Ingredients
1 bowl (approx. 400 ml) per person as a full keto lunch.
| Amount | Ingredient | Note | ||
|---|---|---|---|---|
| Sardines in olive oil | 2 small cans, drained, keep the bones | |||
| 2 small cans, drained, keep the bones | ||||
| Bone broth | - | |||
| Baby spinach | - | |||
| Garlic cloves | finely chopped | |||
| finely chopped | ||||
| Parmesan | freshly grated | |||
| freshly grated | ||||
| Extra virgin olive oil | approx. 2 tbsp | |||
| approx. 2 tbsp | ||||
| Lemon juice | approx. 1 tbsp | |||
| approx. 1 tbsp | ||||
| Salt and pepper | - | |||
Preparation
Sauté the garlic, bring the bone broth to a boil, let the baby spinach wilt briefly, add the sardines and warm them through. Finish with parmesan and olive oil.
Why are sardines and bone broth the best electrolyte soup base?
Canned sardines (with bones) deliver approx. 380 mg of calcium per 100 g, comparable to milk but without lactose and with added omega-3. The bone broth contributes sodium (depending on the recipe, approx. 0.5 to 1.5 g of salt per liter) and glycine and proline from the collagen, which support the gut lining. Baby spinach adds potassium and magnesium. Parmesan adds more calcium and sodium. Together this soup covers calcium, sodium, potassium and magnesium at just 3 g of net carbs.
Source: USDA FoodData Central, Fish, sardine, Pacific, canned in tomato sauce , NIH Office of Dietary Supplements, Calcium
Eating sardine bones? Why they are the most valuable part
The soft, cooked-in bones of canned sardines are the main source of calcium. They are fully edible, no chewing or choking risk like with fresh fish bones. For maximum calcium, eat the bones deliberately rather than removing them. Sardines packed in olive oil (without tomato) are keto-friendly; versions in tomato sauce can carry slightly more carbs.
Bone broth on keto: more than just sodium
Home-cooked bone broth contains collagen breakdown products (glycine, proline, hydroxyproline) that strengthen the gut lining and serve as precursors for the body's own collagen. Glycine also has a mild calming effect and supports sleep. Home-cooked broth works best for this soup, jarred ready-made broth often contains less collagen.
How do I serve and vary the keto sardine bone broth soup?
In my experience, many people underestimate sardine soup, it sounds unspectacular but tastes deep and complex thanks to the bone broth, parmesan and olive oil. In practice it is one of the most effortless electrolyte soups because sardines are always within reach in the pantry.
Meal prep: prepare the broth, sardines fresh each day
Bone broth can be cooked in large batches and kept in the fridge for up to 5 days (or frozen). Always use sardines straight from the can, they do not need to be cooked, only warmed through in the hot broth. This keeps the sardine texture better than long cooking.
Variation: Mediterranean version with capers and olives
Add 1 tbsp capers and 5 to 6 black olives. Capers bring quercetin and extra sodium, olives bring oleic acid and potassium. The soup takes on a Mediterranean, puttanesca-style character. Carbs stay below 4 g net carbs.
Which tips make the keto sardine bone broth soup better?
- Buy sardines in olive oil (not in tomato), fewer carbs, more fat, more intense flavor.
- Never leave sardines in the hot broth longer than 2 minutes, otherwise they soften and fall apart.
- Make the bone broth yourself or choose a quality ready-made option, cheap supermarket broth contains barely any collagen.
- Grate the parmesan over the soup only after serving, it then melts on the hot broth.
- Drizzle a splash of good olive oil over the finished soup, it rounds out the flavors and bumps up the fat.
Nutrition values
| Nutrient | Per 100 g | Per serving | Keto rating |
|---|---|---|---|
| Calories | approx. 78 kcal | approx. 280 kcal | Moderate. A full meal for lunch. |
| Moderate. A full meal for lunch. | |||
| Fat | approx. 4 g | approx. 14 g | Good for keto. Sardines, olive oil and parmesan. |
| Good for keto. Sardines, olive oil and parmesan. | |||
| Net carbs | approx. 0.8 g | approx. 3 g | Very good for keto. Spinach is the main carb source. |
| Very good for keto. Spinach is the main carb source. | |||
| Sugar | approx. 0.3 g | approx. 1.1 g | Very low. |
| Very low. | |||
| Protein | approx. 7.8 g | approx. 28 g | High. Sardines are very protein-rich. |
| High. Sardines are very protein-rich. | |||
| Salt | approx. 0.8 g | approx. 2.9 g | High. Bone broth, sardines and parmesan as sodium sources. |
| High. Bone broth, sardines and parmesan as sodium sources. | |||
Note: Nutrition values are estimated averages per 100 g and per serving and may vary depending on ingredients, brands, portion size, and preparation. They do not replace individual nutrition or medical advice.
FAQ
How much calcium does one serving of this soup provide?
Sardines (150 g with bones) deliver approx. 570 mg of calcium, parmesan (20 g) approx. 230 mg, together about 800 mg of calcium per serving. That covers roughly 80% of the recommended daily intake (1,000 mg/day for adults). This makes the soup one of the richest non-dairy calcium sources in a keto diet.
Do I need to remove the bones from the sardines?
No, and it is better to keep them. The soft, cooked-in bones of canned sardines are fully edible and hold most of the calcium. They are nothing like raw fish bones, they crush easily when chewed.
Can I make the soup with fresh sardines?
Yes, but it is more work. Fresh sardines need to be gutted, filleted and cooked separately. The calcium from the bones is lost, since fresh sardine bones are not edible. For the electrolyte benefit, canned sardines are the more practical choice, and for calcium they are the more effective one.
How long does homemade bone broth keep?
In the fridge for 4 to 5 days. In the freezer, portioned (for example in ice cube trays or jars), up to 3 months. Do not refreeze thawed bone broth.