to $708.3 million, primarily due to double-digit net sales increases from Canada and Europe and low single digit net sales increases from the US, United Kingdom and Hain Pure Protein segments.
"Our first quarter results were solid with improved net sales growth and profitability, meeting our expectations across our business segments," said Irwin D. Simon, founder, president and chief executive officer of Hain Celestial. "Importantly, we are on track to build momentum throughout the year as our execution of Project Terra continues to drive incremental sales growth and margin improvement to deliver long-term sustainable stockholder value."
Net sales increased 4% to $708.3 million compared to the prior year period, or 3% on a constant currency basis, primarily reflecting double digit net sales increases from Canada and Europe and low single digit net sales increases from the United States, United Kingdom and Hain Pure Protein segments. Gross margin as a percentage of net sales of 18.6%; adjusted gross margin of 19.1%. Operating income of $31.5 million; adjusted operating income of $39.7 million.
Net income of $19.8 million, an increase of 131% over the prior year period; adjusted net income of $23.7 million, an increase of 59% over the prior year period.
Net sales for Hain Celestial United States increased 4% to $263.7 million over the prior year period, reflecting growth from the Pure Personal Care, Better-for-You Baby and Better-for-You Pantry platforms including Alba Botanica, Jason, Avalon Organics, Live Clean; Earth's Best; Spectrum and Imagine brands; partially offset by declines in Fresh Living with The Greek Gods brand, Better-for-You-Snacking with Garden of Eatin' brand and Tea with Celestial Seasonings brand.
Net sales for Hain Celestial United Kingdom increased 1% to $222.4 million over the prior year period, reflecting 8% growth from Tilda and Ella's Kitchen, partially offset by a 1% decrease from Hain Daniels.
Net sales for Hain Pure Protein increased 2% to $119.1 million over the prior year period, reflecting a 6% increase from the combined FreeBird and Plainville Farms businesses while the Empire Kosher business net sales declined 6% with more sales attributable in the prior year period due to the timing of the Jewish holidays.
Net sales for Rest of World increased 14% to $103.1 million over the prior year period, or 9% on a constant currency basis driven by 13% growth from Hain Celestial Canada from Yves Veggie Cuisine, Sensible Portions, Live Clean and Tilda brands and 10% growth from Hain Celestial Europe from Danival and Joya brands and own label.
The company reiterated its annual guidance for fiscal year 2018, including a 4-6% increase in sales to $2.967 billion to $3.036 billion; adjusted EBITDA of $350 million to $375 million, an increase of approximately 27% to 36% as compared to fiscal year 2017.