How to Help a Dog Gain Weight Healthily

At a glance

• Always get a vet check first — unexplained weight loss can signal illness, parasites, or malabsorption
• Increase calories gradually, not all at once — a sudden jump in food intake can cause digestive upset
• High-quality protein is the most important nutrient for building lean muscle, not just adding bulk
• Feeding frequency matters — 3 smaller meals a day is more effective than one large one for underweight dogs
• Aim for a steady gain of 1–2% of body weight per week, not a rapid increase

Why is my dog underweight?

The most important first step to helping a dog gain weight is understanding why they're underweight in the first place. Simply feeding more food before knowing the cause is putting the cart before the horse.

Common reasons include:

• Insufficient food — portion sizes that don't match their actual energy needs
• High activity levels — working dogs, sporting breeds, and young dogs burn considerably more calories
• Recent illness or recovery — the body uses more energy healing than at rest
• Intestinal worms or parasites — these compete directly for nutrients from food
• Poor food quality — diets high in filler ingredients and low in digestible protein leave dogs nutritionally underfed even when the bowl looks full
• Underlying health conditions — thyroid problems, exocrine pancreatic insufficiency (EPI, where the pancreas doesn't produce enough digestive enzymes), or inflammatory bowel disease

If your dog has lost weight without an obvious explanation, or is struggling to maintain weight despite eating well, see a vet before changing their diet. Unexplained weight loss that continues over several weeks warrants a proper investigation.

What should I feed an underweight dog?

Protein is the foundation of healthy weight gain in dogs. Not all calories are equal. Calories from quality protein build lean muscle tissue. Calories from low-grade starch and filler ingredients add fat and little else.

Look for food where a named meat source — chicken, beef, lamb, salmon — sits at the top of the ingredients list. Different proteins offer slightly different amino acid profiles, so variety over time is beneficial. Amino acids are the building blocks proteins are made from — the better the protein source, the more usable building blocks reach your dog's muscles.

Fat is also important. It's the most calorie-dense macronutrient, providing around twice the energy of protein or carbohydrate per gram. Healthy fat sources like salmon oil, chicken fat, and lamb naturally increase calorie density without requiring you to double portion sizes. Adding an omega oil to meals is a practical way to boost calorie intake while supporting skin and coat condition at the same time.

Marleybones meals are vet-developed and built around high-quality named meat proteins, with no fillers diluting the nutritional content. For an underweight dog, that means more of each meal is actually working — going toward muscle and tissue rather than passing straight through.

Avoid heavily processed foods that rely on meat and animal derivatives rather than named meat. Reading the ingredients label carefully tells you far more about what your dog is actually eating than the marketing on the front of the pack.

How much more should I feed an underweight dog?

Start by calculating the recommended daily amount for your dog's target weight, not their current weight. Most feeding guides are based on ideal body weight — using current weight means you're feeding to maintain a body condition you're trying to change.

Increase portions by 10% per week rather than jumping straight to the new total. This gives the digestive system time to adapt. Splitting the daily ration into 3 meals rather than 1 or 2 makes each meal easier to digest and keeps energy levels steadier through the day.

If your dog has a sensitive stomach or a history of digestive issues, transitioning to a new food gradually is especially important. Introducing any dietary change too quickly is one of the most common causes of loose stools and food refusal in dogs trying to gain weight.

Track progress weekly. Weigh your dog at the same time of day, ideally before a meal. You're aiming for roughly 1–2% of body weight gained per week. For a 10kg dog, that's 100–200g per week. Faster than this and you risk adding fat rather than lean muscle.

Are there other factors that affect weight gain?

Food quality and quantity do most of the work, but a few other factors are worth considering.

Gut health matters more than most owners realise. If your dog's gut isn't absorbing nutrients efficiently, they can eat the right food in the right quantities and still struggle to gain weight. A healthy gut microbiome — the community of bacteria living in the digestive tract — improves nutrient absorption significantly. Prebiotic fibre from ingredients like chicory root feeds the beneficial bacteria and helps maintain that balance. Marleybones includes chicory root in every recipe for exactly this reason.

Stress and anxiety reduce appetite and interfere with digestion. Dogs in high-stress environments, recently rehomed dogs, or those recovering from trauma often eat less and absorb nutrients less effectively. Addressing the root cause matters as much as the food itself.

Finally, exercise. Resistance-style activity — walking uphill, swimming, playing fetch — builds muscle rather than simply burning calories. Light, consistent exercise is a useful complement to a higher-protein diet when the goal is lean weight gain rather than fat gain.

Every dog is different — build your personalised Marleybones feeding and health plan tailored to your dog's age, size, and health requirements.

“Such a relief to see her enjoying her food”

Get 40% OFF today

Use code: FRESH40

FAQs

How long does it take for an underweight dog to gain weight?

At a healthy rate of 1–2% body weight per week, a dog that is 10% underweight should reach their target in around 5–10 weeks. Slower progress is fine. Rushing weight gain risks adding fat rather than lean muscle.

Can I add anything to my dog's food to increase calories?

Yes. Healthy additions include a splash of omega oil, a spoonful of plain cooked egg, or small amounts of plain cooked meat added as a topper. Avoid adding human foods that are high in salt, sugar, or seasoning. Omega oil is particularly useful as it's calorie-dense and supports coat and skin health at the same time.

Is fresh food better for underweight dogs than kibble?

Fresh food tends to be higher in digestible protein and moisture, both of which support efficient nutrient absorption. For dogs that are underweight due to poor absorption or digestive issues, switching to a more digestible format is often part of the solution. Marleybones Pantry Fresh meals are freshly prepared with no fillers, making them a practical option for dogs that need to get more from every meal.

Should I be worried if my dog won't eat enough to gain weight?

A dog consistently refusing food or eating well but still losing weight needs a vet assessment. This can point to dental pain making eating uncomfortable, nausea from an underlying condition, or absorption issues like EPI. Don't assume it's fussiness without ruling out a physical cause first.

What body condition score should I aim for?

Vets use a body condition score (BCS) on a scale of 1–9, where 4–5 is ideal. At a healthy weight, you should be able to feel your dog's ribs easily without pressing hard, but not see them prominently. The waist should be visible from above, and there should be a slight tuck in the abdomen when viewed from the side. Ask your vet to score your dog at their next check-up.

“A complete game changer!!”

Get 40% OFF today

Use code: FRESH40