Pumpkin is loaded with carbs (basically, sugar) which becomes fat if not burned within a short amount of time.
http://www.nutritiondata.com/facts/vegetables-and-vegetable-products/2918/2 Whole Dog Journal reported (in the grain free issue this year) that dogs with weight control issues will struggle more on high carb foods. This has been my experience as well. So I really watch carbs with my senior (who tends to gain weight by looking at food).
It's not just about calories; it's about what comprises the food and what bodies do with them. In addition to cutting back her grain free kibble (Instinct) I supplement boiled boneless skinless chicken breast
http://www.nutritiondata.com/facts/poultry-products/701/2, and some green beans
http://www.nutritiondata.com/facts/vegetables-and-vegetable-products/2342/2 (lower in carbs than the pumpkin, high in fiber). For treats, I give boiled chicken pieces, some meat jerky snacks, or a few Cheerios
http://www.nutritiondata.com/facts/breakfast-cereals/1522/2 (high in fiber) which help her feel filled up and she likes the crunchiness. Yes, she works for a single Cheerio at a time.
So does my GSD and my pup!
After she eats, we go for a short walk around the neighborhood, so that the food isn't just sitting there, waiting to convert to fat. We increased her overall activity level as much as we reasonably can.
She's been on this diet since mid-December and she lost 10% of her body weight (we just weighed in yesterday, when she got her nails trimmed at the vet's) and has kept it off.